Biaxially stretched polyamide resin film

ABSTRACT

Disclosed is a polyamide resin film which has excellent dimensional stability with respect to moisture absorption, excellent mechanical characteristics and sliding properties under high temperature and high humidity conditions, and excellent handling properties. Specifically disclosed is a biaxially stretched polyamide resin film, to which 0.3-10% by weight of an inorganic material including a layered compound is added. The biaxially stretched polyamide resin film is characterized in that the layered compound is in-plane oriented, and that the film has a haze of 1.0-20%, an elastic modulus in the longitudinal direction of 1.7-3.5 GPa at a relative humidity (RH) of 35%, a surface roughness (Sa) of 0.01-0.1 μm, and a coefficient of static friction (F/B) of 0.3-1.0 at a normal stress of 0.5 N/cm 2 .

TECHNICAL FIELD

The first invention relates to a film of a resin containing a layeredcompound commonly called as a nano-composite. More particularly, theinvention relates to a stretched film of a nano-composite polyamideresin of which stretching at a high ratio has conventionally been saidto be impossible with an addition amount of 1% or more.

A conventional nylon film is made easy to slide by roughening thesurface in the case the slipping property is needed under high humiditysince the slipping property is changed in accordance with humidity;however in the case of a film using an inorganic layered compound, thealteration of the slipping property according to humidity is small andalso even if the surface roughness is small, a sufficient slippingproperty can be exhibited and therefore contradictory characteristicssuch as gloss can be satisfied simultaneously.

The second invention relates to a biaxially stretched multilayerpolyamide resin film preferably usable for wrapping of retort foodproducts etc. while being laminated with an olefin resin film such aspolyethylene, polypropylene, or the like, tough and excellent in pinholeresistance, and having a multilayer structure. More particularly, theinvention relates to a biaxially stretched multilayer polyamide resinfilm with little boiling strain in the entire width of a film roll inthe case of using the resin film as a wrapping material.

The shrinkage stress can be lowered by providing the above-mentionedmultilayer structure to the second invention and as a result, bowing tobe a cause of the strain at the time of boiling can be suppressed.Further, in the case a layered compound is added simultaneously, the gasbarrier property can be improved and the boiling strain can be lessenedsimultaneously.

BACKGROUND ART

A biaxially stretched polyamide resin film is excellent in themechanical characteristics, barrier property, pinhole resistance,transparency, etc. and has been used widely as a wrapping material.However, due to a high hygroscopic property derived from amide bonds inthe polymer structure, the mechanical strength is fluctuated and thehygroscopic elongation occurs in accordance with humidity fluctuationand besides, problems tend to occur in many kinds of steps. Furthermore,the glass transition temperature of the resin itself is not so high andimprovement of heat resistance, particularly, the mechanical propertiesat a high temperature has been desired.

Moreover, a common polyamide film made of nylon 6 has a high elasticmodulus but low elongation and accordingly shows a lowered maximum pointstress and rather brittle characteristics in a low humidity and on theother hand, the polyamide film has a low elastic modulus but highelongation and accordingly shows an increased maximum point stress andductility in a high humidity. In stretching condition for improving thecharacteristics in lower humidity side, there occurs a problem that thefilm characteristics are unbalanced. As described, a common polyamidefilm shows considerably changed characteristics in accordance withhumidity as compared with a film made of a poly(ethylene terephthalate).Therefore, it is required to control the humidity in the process and todetermine the processing conditions on the basis of previous estimationof characteristic fluctuation.

Further, a biaxially stretched polyamide resin film shows decrease ofthe mechanical strength and occurrence of hygroscopic elongation due tothe high hygroscopic property derived from amide bonds in the polymerstructure and, in addition, tends to cause problems in many steps due tostrains and curls formed due to the difference of shrinkage quantitiesat the time of boiling.

The stains at the time of humidity absorption and boiling are generateddue to relaxation of the structure at the time of stretching. When amaterial with a high stretching stress is stretched, there is a relationbetween that the shrinkage stress generated at the time of relaxationbecomes high and that the stain also becomes significant. Therefore, itis supposed to be possible that the strain or the like can be suppressedby lowering the shrinkage stress; however in the case of a polyamideresin, it becomes difficult to change the stretching stress due to thestrong hydrogen bonds between molecules and thus it is difficult tolower the stretching stress. Some of previous documents disclosedecrease of boiling strains; however there is no technique disclosed forlowering the stress (Reference to Patent Documents 1 to 3).

-   Patent Document 1; Japanese Patent Application Laid-Open (JP-A) No.    2006-96801-   Patent Document 2: JP-A No. 2006-88690-   Patent Document 3: JP-A No. 2007-237640

As described above, with respect to a polyamide resin film with loweredboiling strains, there is no investigation on lowering the boilingstrains, while paying attention to the stretching stress.

Further, it has been known as a method for improving heat resistance andhygroscopic property of a polyamide resin that a layered silicate isevenly dispersed and this technique has been known well asnano-composite formation. Since the above-mentioned variouscharacteristics can be improved by the nano-composite formation, it isexpected that a film with improved characteristics can be obtained byfilm formation; however, actually, the resin is generally poor in thestretching property and unsuitable as a resin for stretched films.Particularly, it is said that in order to sufficiently heighten theeffects of mechanical characteristic improvements, addition of 1% ormore of a layered silicate to the polyamide resin is needed; however thestretching of a polyamide resin with a high layered silicate content isconsiderably difficult.

Patent Document 4 discloses a biaxially stretched polyamide filmcontaining a layered silicate and it is made indispensable that thehighest reaching temperature for the successive stretching in the widthdirection followed by the longitudinal direction for overcoming thedifficulty of stretching is so high as 180 to 200° C. and not onlydifficulty of production but also crystallization is promoted too farbefore sufficient stretching in the width direction is performed, sothat there occur problems that the layered silicate cannot besufficiently oriented; that various effects due to the addition of thelayered silicate are not exhibited; that thickness unevenness occurs infine regions; and that pinhole resistance cannot be satisfied.

-   Patent Document 4: JP-A No. 2003-20349

Further, as being understood from the scopes of claims of the specifiedmethods described above, practically the amount is 1 wt. % or lower(including the organic matter contained in the interlayer) and if itexceeds 1 wt. %, whitening at the time of stretching and poorproductivity at the time of high stretching ratio are pointed out. Thecauses for them are supposedly attributed to that the stress tends to beconverged on the tip end of the layered compound at the time ofstretching and creases and cracks are easily caused.

Further, Patent Document 5 discloses a patent of a stretched film in asystem containing 0.5 to 5% of a layered inorganic compound but neitherdescribes any concrete countermeasure for solving the above-mentionedpoor stretching property nor discloses any technique for a stretchingmethod with industrial productivity by successive biaxial stretching ina system containing a layered compound in a high concentration of 1% orhigher and consequently, results in investigation in a level ofsimultaneous biaxial stretching of small specimens in a laboratory.Also, there is a description in the specification that a layeredinorganic compound such as montmorillonite has an effect on improvementof the slipping property due to shutting of water absorption property;however, an equilibrium moisture content of a resin is increased if amaterial such as montmorillonite is added to a nylon resin. Based onthis, it can be said that the essence of the invention is significantlyattributed to the effect of the addition of the inorganic lubricant.

-   Patent Document 5: JP-A 2003-313322

On the other hand, Nishino et al, Kobe University pointed out aninteresting result with respect to evaluation of orientation of alayered inorganic compound dispersed in a stretched film (e.g.,Non-patent Document 1). In this report, they paid attention to 060reflection in a layer of montmorillonite and pointed out that thereflection intensity was increased in the meridian direction by in-planeorienting montmorillonite.

-   Non-Patent Document 1: Molecular Nanotechnology 174th Conference,    first Seminar, Preprints, p 22-23, Jul. 13, 2007

Further, with respect to piercing strength, this characteristic can beexhibited by increasing the in-plane orientation of a polyamide resinand if a layered compound is added to further heighten the piercingstrength, contrarily the stretching ratio cannot be increased and thusthere is a problem that the piercing strength is scarcely improved ascompared with that in a system containing no layered inorganic compound.

As described, in the extension of conventional techniques, industrialproduction of stretched films of polyamide resin excellent in variouscharacteristics has been difficult.

Also, generally, for providing the slipping property to films, particlesare added as a lubricant to form projections on the surfaces; however inthe case of a polyamide film, since the resin becomes soft and theslipping property is lowered due to increase of humidity, it is requiredto roughen the surface for achieving also the slipping property evenunder high humidity. Therefore, there occurs a problem of worsening ofthe gloss in a polyamide film having improved slipping property underhigh humidity.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The first invention aims to provide a polyamide resin film excellent indimensional stability with respect to moisture absorption, mechanicalcharacteristics and a slipping property under high humidity and hightemperature, and a handling property, by stretching a polyamide resin inwhich a layered compound represented by a layered silicate is evenlydispersed and which is conventionally difficult to be stretched in thesame stretching conditions as those for a conventional polyamide resincontaining no layered compound. Further, the first invention aims toprovide a film in which a layered compound is high-dimensionallyoriented and which has been conventionally thought be impossible, andthus to provide a biaxially stretched polyamide resin film havingsufficient in-plane orientation although containing a large quantity ofa layered inorganic compound, particularly excellent in mechanicalcharacteristics, a barrier property, heat resistance, dimensionalstability, and a piercing property and little fluctuation of mechanicalcharacteristics due to humidity change.

The second invention aims to provide a biaxially stretched multilayerpolyamide resin film with suppressed boiling strains and excellent inthe dimensional stability and improvement of pinhole resistance bylowering the shrinkage stress caused at the time of boiling by loweringthe stress at the time of stretching and consequently decreasing bowing.

Means to Solve the Problems

Inventors of the invention thought that easy formation of cracks along alayered compound due to stress in the perpendicular direction to theplane of the layered compound was a problem in stretching and madeinvestigations on orientation state of the layered compound and decreaseof the stretching stress and consequently, considered that in aconventional method, a large stress was applied to the molecular chainsin the width and thickness directions at the time of lengthwisestretching of a cast sheet since the molecular chains were fixed by thelayered compound and thus the successive high stretching in the widthdirection was difficult and accordingly found a method for promotingorientation of the layered compound in the in-plane direction by evenlyapplying the shear stress to the sheet at the time of casting andthereby suppressing formation of creases and cracks formed by stressconverged on the tip end of the layered compound and at the same time amethod capable of lowering the entanglement density in the thicknessdirection and further made investigations in detail on causes ofdecrease of the stretching property. Accordingly, paying attention tothe in-plane orientation of the dispersed inorganic layered compoundbesides the resin of the matrix and referring to the report by Nishinoet al, the inventors of the invention quantitatively measured theorientation degree of the layered compound and investigated therelationship of characteristics and consequently found that in a filmobtained by employing such methods, a layered compound could be orientedin a very high level and that a film contained a layered compoundoriented in a high level and had excellent characteristics which aconventional film never had in the case the in-plane orientation degreemeasured from a half width of an x-ray diffraction peak derived from thedispersed layered compound became a specified value or higher and thesefindings now lead to completion of the invention.

That is, the invention has the following configurations.

1. A biaxially stretched polyamide resin film containing 0.3 to 10 wt. %of an inorganic material including a layered compound, in which thelayered compound is in-plane oriented and the film has a haze of 1.0 to20%, an elastic modulus in the longitudinal direction of 1.7 to 3.5 GPaat a relative humidity of 35% RH, a surface roughness (Sa) of 0.01 to0.1 μm, and a static friction coefficient (F/B) of 0.3 to 1.0 at anormal stress of 0.5 N/cm².2. The biaxially stretched polyamide resin film as described in 1,wherein the number of pinholes after 1000 times Gelbo Flex test at 23°C. is 0 to 30.3. The biaxially stretched polyamide resin film as described in 1 or 2,wherein the film is transversely stretched at a transverse stretchingtemperature of 50 to 155° C.4. The biaxially stretched polyamide multilayer film as described in 1,wherein the thermoplastic resin stretched film contains 0.3 to 10 wt. %of the inorganic material including the layered compound and has alaminate structure of 8 or more layers in total and a thickness of 3 to200 μm, and the in-plane orientation degree of the inorganic layeredcompound measured by x-ray diffractometry is in a range of 0.4 to 1.0.5. The biaxially stretched polyamide multilayer film as described in 4,wherein a static mixer method is employed at the time of melt extrusionof a thermoplastic resin and the resin temperature immediately beforeintroduction into the static mixer is in a range from the melting pointto melting point +70° C. and the heater temperature in the latter halfof the static mixer is set to be higher by 5° C. or more and by 40° C.or less than the resin temperature immediately before introduction intothe static mixer.6. The biaxially stretched polyamide resin film containing 0.3 to 10 wt.% of the inorganic material including the layered compound as describedin 1, wherein the layered compound is in-plane oriented and the in-planeorientation (ΔP) of the film is 0.057 to 0.075, and the value ofpiercing strength/thickness of the film is 0.88 to 2.50 (N/μm).7. The biaxially stretched polyamide resin film as described in 6,wherein the stretching ratio on the basis of an area by biaxialstretching measured as the product of the stretching ratio in thelengthwise direction and the stretching ratio in the transversedirection is 8.5 times or more.8. The biaxially stretched polyamide resin film as described in 6 or 7,wherein biaxial stretching is successive biaxial stretching inlengthwise stretching-transverse stretching order and when Ny is definedas a refractive index in the center part in the width direction of thefilm, the difference Ny(A)−Ny(B) between Ny(A) which is Ny of the sheetbefore lengthwise stretching and Ny(B) which is Ny of the sheet afteruniaxial stretching is 0.003 or higher.9. The biaxially stretched polyamide resin film as described in 1,wherein the film contains 0.3 to 10 wt. % of the inorganic materialincluding the layered compound and has a laminate structure of 8 or morelayers, the film is obtained by stretching as much as 2.5 to 5.0 timesin the longitudinal direction and 3.0 to 5.0 times in the widthdirection, and the film has a ratio of the product (X1) of the maximumpoint stress (MPa) and a breaking elongation (%) of a sample stored at ahumidity of 40% for 12 hours and the product (X2) of the maximum pointstress (MPa) and a breaking elongation (%) of a sample stored at arelative humidity of 80% for 12 hours is in a range of 1.0 to 1.5 whenthe maximum point stress and breaking elongation is measured by a methodas described in JIS K 7113 under conditions of a starting length of 40mm, a width of 10 mm, and a deformation rate of 200 mm/min after storageat an equilibrium water absorption ratio of 3.0 to 7.0% and a relativehumidity of 40%.10. A biaxially stretched multilayer polyamide resin film having 8 ormore layers in total and using a same resin composition for 80% based onthe ratio of the number of the layers, wherein the film is stretched 2.5to 5.0 times in the longitudinal direction of the film and has anin-plane orientation coefficient (ΔP) of 0.057 to 0.07 and a strain of0.1 to 2.0% after boiling treatment.11. The biaxially stretched multilayer polyamide resin film as describedin 10, wherein the film contains 0.3 to 10 wt. % of an inorganicmaterial containing a layered compound, the layered compound is in-planeoriented, and the oxygen permeation amount in conversion into 15 μm is0.05 to 18 cc.12. The biaxially stretched multilayer polyamide resin film as describedin 10 or 11, wherein at least one layer or more of resin layerscontaining a polyamide resin having a meta-xylylene skeleton as a maincomponent are laminated.

Effects of the Invention

According to the first invention, a polyamide resin containing a layeredcompound evenly dispersed therein, which has been supposed to bedifficult to obtain with good strength and appearance by a conventionalstretching method, can be stretched evenly without deteriorating theappearance and according to this method, it is made possible to providea polyamide resin film excellent in a slipping property under highhumidity and also excellent in the surface gloss, which is generallydifficult to be satisfied all together.

Also, according to the first invention, it is made possible to provide afilm excellent in various characteristics, particularly, a barrierproperty, mechanical characteristics, a piercing strength, and littlestrength fluctuation in accordance with humidity and made of anano-composite resin containing a layered compound evenly dispersedtherein, which has been supposed to be difficult to obtain with goodstrength and appearance by a conventional stretching method.

Further, with respect to the point that easy occurrence of cleavage inthe thickness direction of a film, which is a problem by multi-layering,this matter can be improved for a multilayer film obtained by a staticmixer method by keeping the resin temperature immediately beforeintroduction into the static mixer is in a range from the melting pointto melting point +70° C. and keeping the heater temperature in thelatter half of the static mixer higher by 5° C. or more and by 40° C. orless than the resin temperature immediately before introduction into thestatic mixer.

According to the second invention, under the conditions for a monolayerpolyamide resin film, a resin sheet having a multilayer structure withthe same composition is stretched to give a film with lessened bowingand little boiling strain even at the end parts in the width direction.Also, use of a resin in which a layered compound is evenly dispersed asa polyamide resin gives a film excellent in not only the boiling strainbut also the barrier property and remarkably usable as a wrappingmaterial. In addition, JP-A No. 2007-196635 is a patent application fora multilayer film; however it does not mention decrease of stress bymultilayer formation at the time of stretching in the publishedspecification and thus the invention is a fact which has not been known.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, at first, the first invention will be described in detail.

(Polyamide Resin)

A polyamide resin to be used in the invention is not particularlylimited and may include a ring-opening polymers of cyclic lactams,condensates of diamines and dicarboxylic acids, and self condensates ofaminoacids and examples are not particularly limited, but are nylon 6,nylon 7, nylon 66, nylon 11, nylon 12, nylon 4, nylon 46, nylon 69,nylon 612, and m-xylylene diamine type nylon. Copolymer type polyamideresins may be also used. Concretely, examples are aromatic polyamideresins such as nylon 6 and nylon 66 copolymerized withm-xylylenediamine, nylon 6T, nylon 6I, nylon 6/6T copolymers, nylon 6/6Icopolymers, nylon 6/polyalkylene glycol resins, nylon 11/polyalkyleneglycol resins, nylon 12/polyalkylene glycol resins, nylon 6/MXD 6copolymers and also usable resins are those obtained by copolymerizationof other components with these resins and preferable examples are nylon6, nylon 66, m-xylylenediamine type nylon. Particularly, the gaspermeability is remarkably decreased by laminating a few layers of am-xylylenediamine type nylon resin and thus it is one of preferableembodiments of the invention.

Further, besides polyamide resin described below, other resins andadditives may be added to these resins for use. Moreover, in terms ofthe economy, one of preferable embodiments is use of a recovered filmproduced by the invention for a part or all of a polyamide resin. Usableexamples of other resins are conventionally known resins such aspolyester resins, polyurethane resins, acrylic resins, polycarbonateresins, polyolefin resins, polyester elastomer resins, and polyamideelastomer resins and not limited thereto.

(Layered Compound)

Examples of the layered compound are not limited to, but are layeredcompounds such as swelling mica, clay, montmorillonite, smectite,hydrotalcite, etc., which are usable regardless of being inorganic andorganic. The form of the layered compound is not particularly limited;however, those having an average length of the longer diameter of 0.01to 50 μm, preferably 0.03 to 20 μm, even more preferably 0.05 to 12 μmand an aspect ratio of 5 to 5000, preferably 10 to 5000 are preferablyused. With respect to the aspect ratio of the layered compound, in thecase the aim for addition is improvement of the barrier property, alayered compound with a high aspect ratio is preferable and in the casethe aim of addition is mechanical reinforcement, a layered compound witha low aspect ratio is preferable.

The addition amount of an inorganic material including a layeredcompound with respect to the above-mentioned polyamide resin ispreferably 0.3 to 10 wt. %. An inorganic layered compound is sometimesadded in form of an organically treated layered compound and theaddition amount and the content (addition amount) of the inorganicmaterial according to the weight residue described below are notnecessarily correspond with each other. Further, if a method formeasuring it from the residue weight as described below is employed, asmall amount of an inorganic material other than the inorganic layeredcompound is added in some cases and in the invention, it is calculatedas the content of the inorganic material including the layered compound.The content of the inorganic material including the layered compound isa value calculated by subtracting the ash from the residue weightmeasured by a thermogravimetric analyzer (TGA) and concretely, it iscalculated by measuring the residue weight after increasing thetemperature of a resin containing a layered compound from roomtemperature to 550° C. and thereafter subtracting the value of resin ashtherefrom. In Example 1, the inorganic content can be measured to be2.6% by subtracting 1.8% of residue weight derived from the resin from4.4% of residue weight by TGA. Also, the ratio of an organic treatmentagent in the layered compound is separately measured by TGA, andcalculation using the numeral value can be employed. The lower limit ofthe addition amount of the inorganic material including a layeredcompound is more preferably 0.3%, furthermore preferably 0.7%, and evenmore preferably 1.0%. If it is less than 0.3%, the effect of the layeredcompound addition is slight in terms of the dimensional stability andmechanical characteristics and thus it is not preferable. Also, thestatic friction coefficient may be increased and the slipping propertymay be worsened. The upper limit is more preferably 10% or less andfurthermore preferably 8% or less. If it is more than 10%, the effect interms of the dimensional stability and mechanical characteristics issaturated and it is not economical and the fluidity at the time ofmelting is lowered and thus it is not preferable. Further, the surfaceroughness becomes unnecessarily significant and the haze may be lowered.

Common layered compounds may be used and organically treatedcommercialized products preferably usable in a monomer insertionpolymerization method described below are Cloisite produced by SouthernClay Products Inc., Somasif and Lucentite produced by Co-op ChemicalCo., Ltd., and S-Ben produced by Hojun Yoko Co., Ltd.

(Thermoplastic Resin Containing Layered Compound Evenly DispersedTherein)

A thermoplastic resin containing a layered compound evenly dispersedtherein is commonly called as a nano-composite resin. The layeredcompound is preferable to be evenly dispersed and not contain coarsematter with a thickness exceeding 2 μM in form of aggregates of thelayered compound. In the case coarse matter with a thickness exceeding 2μm is contained, the transparency is lowered and stretching property islowered and therefore, it is not preferable.

The layered compound is preferable to be evenly dispersed in theabove-mentioned polyamide resin in the invention and its productionmethod can be exemplified as follows.

1. Interlayer insertion method

1) monomer insertion polymerization method

2) polymer insertion method

3) organic lower molecule insertion (organic swelling) kneading method

2. In-situ method: In-situ filler formation method (sol-gel method)3. Ultrafine particle direct dispersion method, etc.

Commercialized materials may include Cress Alon NF 3040 and NF 3020produced by Nanopolymer Composite Corp.; NCH 1015C2 produced by UbeIndustries Ltd.; and Imperm 103 and Imperm 105 produced by Nanocor, Inc.In order to heighten the dispersibility of the layered compound forsuppressing formation of coarse matter of the layered compound containedin the polyamide resin, it is preferable to treat the layered compoundwith various kinds of organic treatment agents; however to avoid anadverse effect of thermal decomposition of a treatment agent at the timeof melt molding, those obtained by using a low molecular weight compoundwith high heat stability or by a method such as the monomer insertionpolymerization method in which a low molecular weight compound is notused are preferable. With respect to the heat stability, a treatedlayered compound having a 5% weight loss temperature of 150° C. orhigher is preferable. TGA or the like can be employed for themeasurement. In the case of a compound with inferior heat stability,foams may be formed in the film or coloring may be caused and therefore,it is not preferable (reference to “Challenging nano-technologicalmaterials: Polymer nano-composites in widened application developments”,Sumitomo Bakelite-Tsutsunaka Techno Co., Ltd.)

The layered compound is preferably in-plane oriented in a film to beobtained for exhibiting characteristics. The in-plane orientation can beconfirmed by observing a cross section by a transmission electronmicroscope or a scanning electronic microscope.

(Film Formation Method)

In stretching of a resin containing a layered inorganic compound in theinvention, problems in the case of stretching by employing successivebiaxial stretching in lengthwise-transverse order, which is generallyadvantageous in terms of economy, are following three points: (1) in thestretching in the lengthwise direction (hereinafter, abbreviated as MD),crystallization proceeds due to the heat at the time of stretching andthe stretching property in the transverse direction (hereinafter,abbreviated as TD) is lost after uniaxial stretching; (2) breakingoccurs at the time of stretching in TD; and (3) breaking occurs at thetime of thermal fixation after stretching in TD. With respect to (1),when the MD stretching conditions in which the TD stretching is possibleand the MD stretching conditions in which the TD stretching isimpossible are put in order, it is found that the refractive index inthe width direction (refractive index in the y-axis, hereinafter,abbreviated as Ny) of a uniaxially stretched sheet after the MDstretching differs from each other. Concretely, it is found that Ny of auniaxially stretched sheet which is TD-stretchable becomes low after theMD stretching, whereas Ny of a uniaxially stretched sheet which is notTD-stretchable (that is, whitened or broken at the time of TDstretching) is scarcely changed or not at all changed after the MDstretching. It is found that in stretching of a common polyamide resin,Ny after the MD stretching becomes low simultaneously with occurrence ofneck-in in the width direction at the time of the MD stretching and onthe other hand, in the case a layered compound is added thereto, neck-inoccurs, but Ny tends to be difficult to be low due to the interaction ofthe layered compound and polyamide resin molecules. The phenomenon issupposedly attributed to as follows: since the molecular chains of afilm before stretching are oriented at random in MD and TD directions,force is generated also in the TD direction at the time of stretchingmolecular chains in the MD direction by the MD stretching, and the forceapplied also in the TD direction can be released by the neck-in in theTD direction in the case of stretching of a common polyamide resin; andon the other hand, in the case of the polyamide resin containing alayered compound, since the molecular chains are cramped by the layeredcompound, the force in the TD direction cannot be released and themolecular chains are put in the state as if they are pulled also in theTD direction, and also the layered compound is rotated at the time ofthe MD stretching and therefore, molecules are pulled also in directionsother than the MD direction. That is, the in-plane orientation isalready in a high state after the MD stretching. Therefore, it issupposed that the stretching stress at the time of successively carryingout the TD stretching becomes high and breaking is caused.

As a method for solving this problem, stretching conditions in which Nybecomes small after the MD stretching are employed to make the TDstretching at a high ratio possible without causing breaking in the TDstretching successively carried out thereafter and thus it is madepossible to produce a biaxially stretched polyamide resin film of theinvention in industrial scale.

In the case Ny(A) is defined as the refractive index in the widthdirection before lengthwise stretching and Ny(B) is defined as therefractive index in the width direction after lengthwise stretching,Ny(A)−Ny(B) is preferably 0.001 or higher. It is more preferably 0.002or higher and most preferably 0.003 or higher.

As a method for lowering Ny after uniaxial stretching, a method ofconsiderably lowering the MD stretching rate can be employed; however,besides, it is made possible to exhibit a similar effect bymulti-layering an un-stretched sheet after melt extrusion. That is, theentanglement density of molecular chains is lowered in the thicknessdirection by multi-layering and thus the deformability of the molecularchains is improved and Ny can be lowered and as a result, increase ofin-plane orientation at the time of the MD stretching can be suppressedand the TD stretching property can be improved. The inventors have foundthat biaxial stretching property can be improved by these methods andhave completed a production method with high industrial applicabilityand a stretched film with excellent characteristics.

(Construction of Film)

The biaxially stretched polyamide resin film of the invention can beobtained essentially by stretching an un-stretched polyamide resin sheetcontaining a polyamide resin layer in which a layered compound is evenlydispersed. Basically a sheet with a monolayer construction is alsostretchable, however from an industrial view, it is preferable tostretch a multilayer sheet.

Hereinafter, a case of multilayer formation will be described. Withrespect to the number of all layers and the thickness of a layer, thelower limit of the number of layers is preferably not less than 8 layersand more preferably not less than 16 layers. The upper limit of thenumber of the layers is preferably not more than 10000 layers and morepreferably not more than 5000 layers. If it is less than 8 layers, nostretching property improvement effect is exhibited and the effect ofthe arrangement of the layered compound at the time of melt extrusion islowered and therefore, it is not preferable. On the other hand, if itexceeds 10000 layers, the effect of stretching property improvement issaturated and the heat shrinkage ratio is lowered and therefore, it isnot preferable.

The lower limit of the thickness of a layer is preferably 10 nm and morepreferably 100 nm in the state before stretching. If it is thinner than10 nm, the crystal size in the layer becomes too small and the heatshrinkage ratio becomes high and therefore, it is not preferable.

The upper limit of the thickness of the layer is preferably not morethan 30 μm and more preferably not more than 20 μm. If it exceeds 30 μm,the in-plane orientation of the layered compound in the state beforestretching is low and the effect on decrease of the stretching stress issmall and therefore it is not preferable.

(Laminating Method)

At the time of multi-layering of the above-mentioned polyamide resin inthe invention, besides laminating different kinds of resin as employedcommonly, it is possible to layer the same kind resin. Herein, althoughit seems to be difficult to find the physical meaning of multi-layeringwith the same kind resin by a method described below; however, in anactual system, an interface of layers does not disappear even in thecase of the same resin is laminated by melt extrusion at the sametemperature and it exists even after stretching. It is the same as thata welded line of an injection-molded product is difficult to beeliminated. As described, even the same type resin is used, multilayerstate is maintained and the entanglement of molecules in the thicknessdirection can be suppressed and kept low. A method for confirming theexistence of an interface of layers at the time of laminating of thesame kind resin by melt extrusion may be a method of cooling a samplewith ice or liquefied nitrogen, producing a cross section by cutting thesample with a razor or the like thereafter, immersing the obtainedsample in a solvent such as acetone, and observing the cross sectionwith a microscope.

A polyamide resin and a resin composition composing other layers basedon necessity are supplied separately to respective extruders andextruded at a temperature higher than melting temperature and themelting temperature is preferably lower by 5° C. than the decompositionstarting temperature. Further, to suppress cracking of the layeredcompound in the resin, the melting conditions and melting temperaturehave to be set carefully. In the case of a polyamide resin with a highmolecular weight, the layered compound is cracked if melting at such alow temperature as not higher than melting point +10° C. is carried out,and the aspect ratio becomes smaller than that in the initial state andthus the effect of use of the layered compound with a high aspect ratiois diminished and therefore, it is preferable to carry out melting at ahigh temperature in a range with no problem in terms of heat stability.

A polyamide resin and a resin composition composing other layers basedon necessity are laminated by various kinds of methods and a feed-blockmethod and a multi-manifold method can be employed. In the case of thefeed-block method, at the time of widening the width to the die widthafter laminating, if the melt viscosity difference between laminatedlayers and the temperature difference at the time of laminating aresignificant, they result in laminating unevenness, deterioration of theappearance, and unevenness of the thickness and therefore, they shouldbe carefully controlled at the time of production. For suppression ofoccurrence of unevenness, it is preferable to control the melt viscosityat the time of extrusion by (1) lowering the temperature and (2) addingvarious kinds of additives such as polyfunctional epoxy compounds,isocyanate compounds, carbodiimide compounds, etc.

In the invention, promotion of orientation in the plane of the layeredcompound by the shear force at the time of laminating is also effectiveto suppress the breaking by convergence of the stress to the tip end ofthe layered compound at the time of stretching. As a method suitable forsuch a purpose, laminating by a feed block method and a static mixermethod is preferable and in terms of the simplicity of facilities, thestatic mixer method is particularly preferable.

In the case of multi-layering by the static mixer method, it ispreferable that the resin temperature immediately before introductioninto the static mixer is in a range from the melting point to meltingpoint +70° C. and that the heater temperature in the latter half of thestatic mixer is set to be in a range of higher by 5° C. or more and by40° C. or less than the resin temperature immediately beforeintroduction into the static mixer. If it is lower than the meltingpoint in the state before introduction into the static mixer, the meltviscosity is too high and the appearance is deteriorated and thelaminated state is disordered and therefore, it is not preferable.Further, if it is a temperature as high as the melting temperature +70°C. or higher, the melt viscosity is too low and the force needed forcausing the above-mentioned stretching effect of the layered compoundbecomes low and therefore, it is not preferable. Moreover, it ispreferable that the heater temperature in the latter half of the staticmixer is set to be higher than the resin temperature immediately beforeintroduction into the static mixer. If the temperature difference islower than 5° C., it results in appearance deterioration such asstreaking unevenness and formation of a portion with a thin thickness,which is a cause of breaking, and therefore, it is not preferable. If itexceeds 40° C., the melt viscosity is too low and the force needed forcausing the above-mentioned stretching effect of the layered compoundbecomes low and therefore, it is not preferable. The melting temperaturedifference between respective layers at the time of laminating athermoplastic resin is 70° C. or lower, preferably 50° C. or lower, andmore preferably 30° C. or lower. The melt viscosity difference betweenrespective layers is within 30 times, preferably within 20 times, andmore preferably within 10 times at the estimated shear rate in a die, sothat appearance control at the time of laminating and unevennesssuppression are made possible. For adjustment of the melt viscosity,addition of the above-mentioned polyfunctional compounds can beemployed. The static mixer temperature or feed block temperature at thetime of laminating is indispensably lower than the 5% decompositiontemperature of the resin and further, it is in a range of preferablymelting point +20 to melting point +150° C., more preferably meltingpoint +30 to melting point +120° C., and most preferably melting point+40 to melting point +110° C. In the case the feed block temperature istoo low, the melt viscosity becomes too high and the load on theextruder becomes too high and therefore, it is not preferable. In thecase the temperature is high, the viscosity is too low and laminatingunevenness occurs and therefore, it is not preferable. Further, the filmafter biaxial stretching tends to have cleavage due to themulti-layering and in this case, the temperature of the latter half partof the static mixer and feed block and the temperature of dies are sosufficiently high as to increase the entanglement of the molecularchains in the interlayer and therefore it can be improved. Concretely,in the case of a static mixer, the cleavage suppression effect can beexhibited by increasing the outlet temperature to be higher by 5 to 40°C. than the inlet temperature.

Further, laminating is possible by a multi-manifold method and theabove-mentioned problem of laminating unevenness is hardly caused;however, in the case of laminating a layer with a melt viscositydifference, there occurs a problem of a turning-around failure of theresins in the respective layers in the end parts and unevenness of thelaminating ratio in the end parts in terms of productivity and also inthis case, it is preferable to control the melt viscosity difference.

For the die temperature, it is the same as described above and it is ina range of 150 to 300° C., preferably 170 to 290° C., and morepreferably 180 to 285° C. If the temperature becomes too low, the meltviscosity becomes too high and the surface roughening occurs to resultin appearance deterioration. If the temperature becomes too high,thermal decomposition of the resin is caused and in addition to that, asdescribed, the melt viscosity difference becomes wide and unevenness iscaused and particularly, unevenness with small pitches is caused andtherefore, it is not preferable.

With respect to each layer before stretching, the thickness of eachlayer is preferably in a range of 0.01 to 30 μm. If the thickness ofeach resin layer exceeds 30 the effect of improving the stretchingproperty is lowered and therefore, it is not preferable for theinvention. If it is less than 0.01 μm, the heat shrinkage ratio afterthermal fixation becomes high and it becomes difficult to keep goodbalance among various characteristics and therefore, it is notpreferable.

(Stretching Method)

For a biaxially stretched polyamide resin film of the invention, anun-stretched sheet extruded by melt extrusion from a T die can bestretched by successive biaxial stretching or simultaneous biaxialstretching, and in addition, a method such as a tubular manner can beemployed; however to carry out sufficient orientation, a method using abiaxial stretching apparatus is preferable. In terms of thecharacteristics and economy, a preferable method is a method ofstretching in the lengthwise direction by a roll type stretchingapparatus and thereafter stretching in the transverse direction by atenter type stretching apparatus (successive biaxial stretching method).Further, with respect to the MD stretching, it is described above thatit is preferable to lower Ny at the time of the MD stretching forimproving the TD stretching property. In order to lower Ny whileincreasing the MD stretching ratio, it is preferable to employmulti-step MD stretching.

It is preferable to obtain the film by stretching a substantiallyun-oriented polyamide resin sheet obtained by melt extrusion from a Tdie 2.5 to 10 times as large in the lengthwise direction at atemperature equal to or higher than the glass transition temperature Tg°C. of the polyamide resin and not higher than 150° C.; thereafterstretching the lengthwise stretched film 3.0 to 10 times as large in thetransverse direction at a temperature of not lower than 50° C. and nothigher than 155° C. of polyamide resins, and successively, thermallyfixing the biaxially stretched polyamide resin film in a temperaturerange of 150 to 250° C.

The heating crystallization temperature can be measured by increasingthe temperature of a sample resin which has been quenched after meltingby DSC.

In the MD stretching, if the temperature of the film is lower than theglass transition temperature (Tg) of the polyamide, problems of breakingand unevenness of the thickness due to the oriented crystallization bystretching occurs. On the other hand, if the film temperature exceeds150° C., breaking is caused due to the crystallization by heat andtherefore, it is not proper. Further, if the stretching ratio in the MDstretching is less than 1.1 times, problems of quality inferiority suchas unevenness of the thickness and insufficient strength in thelengthwise direction are caused and if it exceeds 10 times, there occursa problem that successive TD stretching becomes difficult. Thestretching ratio is preferably 3.0 to 5.0 times.

Further, in the case the film temperature in the TD stretching is a lowtemperature of less than 50° C., the TD stretching property is bad andbreaking occurs and unevenness of the thickness in the TD directionattributed to the neck stretching becomes significant and therefore, itis not preferable. On the other hand, in the case the film temperatureis a high temperature beyond (Tm)−20° C., unevenness of the thicknessbecomes significant and therefore, it is not preferable. Further, if theTD stretching ratio is less than 1.1 times, unevenness of the thicknessin the TD direction becomes significant and it is not preferable and thestrength in the TD direction is lowered and in addition, the in-planeorientation becomes inferior, which results in worsening of thecharacteristics not only in the TD direction but also in the MDdirection and therefore, it is not preferable. The stretching ratio ispreferably 3 times or more. On the other hand, if the TD stretchingratio is a high ratio beyond 10 times, practical stretching isdifficult. The TD stretching ratio is preferably 3.0 to 5.0 times.

With respect to the stretching temperature, stretching at a lowtemperature is preferable in terms of sufficient exhibition of theaddition effect of the layered silicate, unevenness of thickness of thefilm, and Gelbo Flex resistance. A preferable condition may bestretching at a film temperature of 155° C. or lower at the time ofstretching.

Further, the film thickness after stretching is preferably in a range of3 to 200 μm. If it is lower than 3 μm, the handling of the film isworsened and therefore, it is not preferable. If it exceeds 200 μM, theeffect of inorganic composite formation is diminished and therefore, itis not preferable.

A preferable production method of the invention may be a method bycutting both end parts of an un-stretched sheet, which is multi-layeredby a static mixer method or a feed block method, in the width directionby a method of cutting off based on necessity, adjusting the thicknessof each laminated layer to be 30 μm or thinner at the most end partbefore stretching, and thereafter carrying out stretching at least inone direction. In the above-mentioned multi-layer formation method,although depending on the structure of the dies, due to the imperfectionof division of the layers and the disorder of the layers at the time oflaminating, the number of the layers in the end part is sometimelessened and in this case, the layer thickness of the polyamide resincontaining a layered compound with an inferior stretching property in adispersed state may be inevitably increased. Therefore, the layerthickness becomes thicker than 30 μm and the stretching property of onlythe end part is considerably lowered and at the time of stretching, aphenomenon such as whitening and breaking is sometimes observed in theend part. In the invention, in such a case, for correcting the layerthickness in the end part at the time of production to an aimedthickness, one of preferable production methods is a method of trimmingthe end part of un-stretched sheet and thereafter carrying outstretching.

(Thermal Fixation)

In the case a thermal fixation temperature is a low temperature lowerthan 150° C., the effect of dimensional stability improvement of thefilm by heat is slight and therefore, it is improper. On the other hand,in the case of a high temperature exceeding 250° C., appearancedegradation due to whitening attributed to thermal crystallization ofthe polyamide and decrease of the mechanical strength are caused andtherefore, it is improper.

In addition, the density increase due to crystallization in the thermalfixation after the TD stretching and the accompanying volume shrinkageare caused, and in the case of the resin containing the layeredcompound, the stress to be generated is remarkably high and therefore,stress is applied in the MD direction by sharp heating and it sometimesresults in breaking. Therefore, as a heating method at the time ofthermal fixation, it is preferable to increase the heat quantity step bystep and thus generation of acute shrinkage stress is suppressed. Aconcrete method is exemplified as a method of gradually increasing thetemperature or increasing the air blow amount toward the surrounding ofthe outlet from the surrounding of the inlet of a thermal fixation zoneand is preferably a method of gradually increasing the air blow amountin terms of the heat shrinkage ratio after stretching and thermalfixation.

Further, with respect to the relaxation treatment, taking the balancewith the heat shrinkage ratio in the lengthwise direction intoconsideration, it is preferable to determine the relaxation ratio. Inthe invention, since the change of the dimensional stability withrespect to humidity in the lengthwise direction is small, the relaxationratio is preferably in a range of 0 to 5%. If it exceeds 5%, the effecton decrease of the heat shrinkage ratio in the width direction is slightand therefore, it is not preferable.

Next, a method for considerably lowering the MD stretching rate asanother exemplified method will be described.

The method for considerably lowering the MD stretching rate ispreferable to lower the MD stretching rate of 2000%/min or less. It ismore preferably 1000%/min or less. In such a low rate MD stretching,since it is possible to carry out stretching while loosening themolecular chains cramped by the layered compound, it is supposed that Nyis lowered after the MD stretching. In addition, the conditionsdescribed above can be employed for the temperature of the MDstretching, conditions of the TD stretching, and thermal fixationconditions.

A film obtained in the above-mentioned manner can be used industriallyin various applications in form of a roll film wound around a paper tubeor as it is or after being processed for, for instance, printing orlamination. The width of the roll film is preferably 30 cm or wider. Thelength is preferably 500 m or longer. The upper limit of the width isabout 600 cm and the upper limit of the length is about 20000 m. Thosewith a wide width or a long length immediately after film formation areslit in accordance with the use and commonly, used in form of a rollfilm with a width of 200 cm or narrower and a length of 8000 m orshorter.

(In-Plane Orientation of Polyamide Resin Film)

After the biaxial stretching, thermal fixation, and relaxationtreatment, the polyamide resin film of the invention has an in-planeorientation (ΔP) preferably 0.03 or higher and more preferably 0.05 orhigher. The in-plane orientation can be measured by measuringbirefringence with a refractive index meter and carrying out calculationaccording to the following expression:

ΔP=(Nx+Ny)/2−Nz,

wherein Nx is the refractive index in the longitudinal direction; Ny isthe refractive index in the width direction; and Nz is the refractiveindex in the thickness direction.

The mechanical strength as a film is lowered and therefore, it is notpreferable. Also, if it exceeds 0.07, the productivity is lowered andtherefore, it is not preferable.

After the biaxial stretching, thermal fixation, and relaxationtreatment, the biaxially stretched polyamide resin film of the inventionhas an in-plane orientation (ΔP) of preferably 0.057 to 0.075 andparticularly preferably 0.059 to 0.07. The in-plane orientation can beincreased by increasing the biaxial stretching ratio, particularly theTD stretching ratio. If the in-plane orientation is less than 0.057, thepiercing strength is lowered and therefore, it is not preferable. Also,if it exceeds 0.075, the productivity is lowered and therefore, it isnot so preferable.

(Film Characteristics-Piercing Strength)

The piercing strength of the biaxially stretched polyamide resin film ofthe invention is preferable to have a value satisfying a relationalexpression of piercing strength/thickness (N/μm)=0.80 to 2.0. If thepiercing strength is less than 0.80 N/μm, the piercing strength is lowand not preferable for the aim of the invention. Further, it is morepreferably 0.90 or higher. The upper limit is preferably 1.80 or lower.In the case of a production condition of exceeding 1.80, the operationalproperty is lowered and therefore, it is not preferable.

The piercing strength is improved by both of the effect of the layeredcompound and the effect of heightening the in-plane orientation. Forimprovement of the piercing strength, it is preferable to increase theaddition amount of the layered compound and simultaneously heighten thein-plane orientation. It is preferable to satisfy at least the conditionthat the layered compound addition is 0.3% or more and the in-planeorientation is 0.057 or higher. To obtain a film with a high piercingstrength, as described above, the stretching ratio based on the areaafter the biaxial stretching is adjusted to be preferably 8.5 times orhigher and further preferably 12 times or higher. If it is less than 8.5times, the in-plane orientation is not heightened and the piercingstrength is not improved and therefore, it is not preferable. Also, thestretching ratio based on the area is preferably in a range of 8.5 to 40times and if it exceeds 40 times, the operational property is worsenedand therefore, it is not preferable.

(Film Characteristic-in-Plane Orientation of Inorganic Layered Compound)

The film of the invention is improved in the heat resistance, barrierproperty, dimensional stability, and mechanical characteristics byhighly orienting the layered compound in the plane, and thethermoplastic multilayer film in the invention is preferable to have anin-plane orientation of the layered compound measured by x-raydiffractometry in a range of 0.4 to 1.0. Herein, the in-planeorientation is a numeral value calculated from the half width of the(0n0) peak of the layered compound according to the followingexpression:

In-plane orientation=(180−half width)/180.

If the in-plane orientation is less than 0.4, the in-plane orientationis low and the effect of the addition of the layered compound isdiminished and therefore, it is not preferable.

To increase the in-plane orientation of the layered compound, stretchingratio of 6 times or more based on the area is preferable and thestretching ratio of 3 times or more in the transverse direction isfurther preferable. If it is less than 6 times based on the area, thearrangement of the layered compound is insufficient and thecharacteristic improvement effect is low. If it exceeds 50 times basedon the area, the difficult in production exceeds the effect andtherefore, it is not preferable in terms of productivity. To obtain afilm having the in-plane orientation (ΔP) of the biaxially stretchedpolyamide resin film of the invention in a range of 0.057 to 0.075 and avalue of the film piercing strength/thickness (N/μm) in a range of 0.88to 2.0, with respect to the stretching ratio of the film, the stretchingratio based on the surface area after biaxial stretching, which iscalculated as the product of the stretching ratios in the longitudinaldirection and in the width direction, is in a range of preferably 8.5 to40 times and more preferably 12 times or more. If it is less than 8.5times, the in-plane orientation is not increased and the piercingstrength is not improved and therefore, it is not preferable.

The multilayer stretched film containing the layered compound arrangedin the plane of the invention is excellent in the heat resistance andmechanical characteristics and with respect to the heat resistance, thetemperature at which the storage elastic modulus starts decreasing nearTg in dynamic viscoelasticity can be shifted to a high temperature sidein some cases. This is attributed to the reinforcing effect ofsuppressing the movement of the molecular chains of the thermoplasticresin by the layered compound and if the arrangement of the layeredcompound is insufficient, the effect is slight.

The multilayer stretched film containing the layered compound arrangedin the plane of the invention is excellent in the barrier property and,for example, with respect to improvement of the oxygen barrier propertyfor the polyamide resin, in the case 0.3 to 15% as an addition amount ofan inorganic material including a layered compound is added to thepolyamide resin, the oxygen permeability (20 to 25 cc/m²/day/atm) of thebiaxially stretched polyamide resin in conversion into 15 μm can belowered to about 5 to 15 cc/m²/day/atm. If it is less than 1%, thebarrier property improvement effect is slight and if it exceeds 10 wt.%, the barrier property improvement effect is saturated and it is noteconomical. The same effect can be confirmed for polyester resins andpolypropylene resins besides the polyamide resin.

(Film Characteristics-Haze)

The haze of the biaxially stretched polyamide resin film of theinvention is preferably in a range of 1.0 to 20%. If the haze at thetime of stretching is 1.0% or lower, stable production becomes difficultand therefore, it is not preferable. If haze exceeds 20%, it becomesdifficult to see contents at the time of use and additionally, thedesign property is deteriorated and therefore, it is not preferable.

The haze in the invention is the total derived from the resin, derivedfrom the inorganic layered compound, and derived from voids formed byseparation of the resin from the inorganic layered compound surface atthe time of stretching and it is preferable to decrease particularlyhaze derived from the voids and for that, the stretching conditions arepreferable to be set carefully. Concretely, in the case the MDtemperature is too low, the haze is increased due to voids formation andtherefore, it is not preferable. Also, in the case the TD temperature istoo high, haze increase is observed due to crystallization andtherefore, it is not preferable. A preferable temperature range is asdescribed above and it can be adjusted with reference to these facts.Further, it can be adjusted in accordance with the size and type of thelayered compound. For example, not only use of the layered compound witha size smaller than the wavelength of visible light makes the haze smallbut also use of the layered compound with a refractive index close tothat of the resin makes the haze small.

(Film Characteristics-Surface Roughness, Static Friction Coefficient)

The biaxially stretched polyamide resin film of the invention ispreferable to have a static friction coefficient (F/B) satisfying in arange of 0.3 to 1.0 at a normal stress of 0.5 N/cm² while having soextremely smooth surface as to have a surface roughness (Sa) of 0.01 to0.1 μm. In general, if the surface roughness is made low to heighten thesurface gloss, the static friction coefficient is increased and filmsare not at all slid on each other particularly in a high humiditycondition, resulting in various kinds of troubles in processes; however,the specific surface smoothness and the slipping property are bothsatisfied all together peculiarly by biaxial stretching the polyamideresin containing an addition amount of 0.3 to 10 wt. % of the inorganicmaterial including a layered compound in the invention at a sufficientarea ratio. This is supposedly attributed to that the effect of thelayered compound addition can be exhibited at a high level and a highelastic modulus can be maintained in a wide range from a low humidity toa high humidity. If the surface roughness is lower than 0.01, theslipping property is sometimes worsened and therefore, it is notpreferable. Also, if it exceeds 0.1 μm, the surface gloss is notdifferent from that of a system to which a common lubricant is added andit does not meet the aim of the invention. In the case the staticfriction coefficient exceeds 1.0, the slipping property is worsened andtherefore, it is not preferable. The lower limit of the static frictioncoefficient is practically lower than 0.3.

The surface roughness can be increased by increasing the addition amountand also it can be adjusted in accordance with the size, form, or thelike of the layered compound to be added. The static frictioncoefficient can be adjusted by the surface roughness and besides, theelastic modulus can be increased by increasing the stretching ratio,particularly the stretching ratio in the width direction and accordinglythe static friction coefficient can be controlled.

Further, that the surface smoothness and the slipping property are bothsatisfied all together without using a powder lubricant such asspherical silica to be used commonly for increasing the slippingproperty is a characteristic of the invention; however it is allowed toadjust the surface roughness and the slipping property by adding apowder lubricant in accordance with the use. In the case of addition,the average particle diameter of the lubricant particles is preferably0.1 to 10 μm and more preferably 0.3 to 5 μm. The average value of theparticle diameter can be measured by measuring the diameter by anelectron microscope and calculating the average. The addition amount ispreferably 1000 ppm or lower and more preferably 700 ppm or lower.

If the average particle diameter is 0.1 μm or less, it is too small foran aim of changing the surface roughness and therefore, it is notpreferable. In the case particles with an average particle diameterexceeding 10 μm are used or in the case the addition amount exceeds 1000ppm, it sometimes becomes difficult to adjust the surface roughness tobe 0.1 μm or less and therefore, it is not preferable.

The surface roughness (Sa) can be properly adjusted to be 0.01 μm to 0.1μm with reference to the above-mentioned preferable ranges. A concreteadjustment method for preventing it from exceeding 0.1 μm may belessening the addition amount in the case the particle diameter islarge; use of particles with large oil supply amount which is easy to bebroken at the time of stretching in the case the particles areagglomerates (secondary particles) of primary particles with a fineparticle size; etc. As the particles, various kind particles such assilica, alumina, zirconia, titania, crosslinked acrylic beads,crosslinked styrene beads, benzoguanamine, etc. may be used.

(Equilibrium Moisture Content)

The Equilibrium Moisture Content of the Biaxially Stretched Multilayerpolyamide resin film of the invention is preferably in a range of 3.0 to7.0%. The equilibrium moisture content becomes higher than that of apolyamide resin film containing no layered compound and it is attributedto that the layered compound has a high water absorption property. Theequilibrium moisture content is changed in accordance with the additionamount of the layered compound and also changed in accordance with thestretching conditions and it tends to be low along with increase of thein-plane orientation, so that the final equilibrium moisture content ofthe film can be determined by the addition amount of the layeredcompound and the stretching conditions. If the equilibrium moisturecontent is less than 3.0%, the elongation in a high humidity is loweredand therefore, it is not preferable. Also, if the equilibrium moisturecontent exceeds 7%, water is evaporated at the time of drying and aproblem by water absorption may be caused at the time of processing andtherefore, it is not preferable.

(Maximum Point Stress, Elongation)

The biaxially stretched multilayer polyamide resin film of the inventionis preferable to have a ratio of the product (X1) of the maximum pointstress (MPa) and a breaking elongation (%) of a sample stored at ahumidity of 40% for 12 hours and a product (X2) at a humidity of 80% ina range of 1.0 to 1.5 when the maximum point stress and breakingelongation is measured by a method as described in JIS K 7113 underconditions of a starting length of 40 mm, a width of 10 mm, and adeformation rate of 200 mm/min after storage at a relative humidity of40%. It is said that the film toughness can be measured by calculatingthe area in the lower side of a stress-strain curve. A common nylon filmhas both of high elongation and high maximum point stress under a highhumidity and is thus a film with extremely high ductility and on theother hand, both maximum point stress and elongation are low at a lowhumidity and practically, it is impossible to design the mechanicalcharacteristics of a film in consideration of the effect of thehumidity. Contrarily, as compared with a common nylon film, theinventors of the invention have found that a film containing the layeredcompound oriented in the plane has characteristics scarcely changedunder a high humidity and is effective to increase the maximum pointstress under a low humidity and the finding leads to completion of theinvention. As a reason for this, it is assumed that addition of amaterial with high hygroscopic property can reinforce the mechanicalcharacteristics under a low humidity and the hygroscopic propertyprovides proper mobility of molecular chains under a high humidity andthus prevents decrease of elongation or the like.

There is poly(ethylene terephthalate) as a film which scarcely affectedby humidity, and in this case, the ratio is around 1.0 and due to thecloseness to 1.0, with respect to the above-mentioned characteristic, itcan be said that the film has low humidity dependence. If the ratioexceeds 1.5, the film become highly humidity-dependent just like acommon nylon film and it does not meet the aim of the invention. To makethe ratio close to 1.0, the above-mentioned stretching conditions,particularly the stretching ratio in the MD direction and the stretchingratio in the TD direction, are important.

Concretely, the MD stretching ratio is preferably 2.5 to 5.0 times andmore preferably 2.8 to 4.5 times. The MD stretching may be a one step ormulti-step process. If the MD ratio is less than 2.8 times, the in-planeorientation after the biaxial stretching is not improved and themechanical characteristics at a low humidity are degraded and therefore,it is not preferable. If it exceeds 5 times, not only characteristicssuch as boiling strain are degraded and the stability at the time ofstretching is lowered and therefore, it is not preferable. The TDstretching ratio is preferably 3.0 to 6.0 times. If it is less than 3.0times, the maximum point stress in MD under a low humidity becomes lowand therefore, it is not preferable and additionally, since the in-planeorientation is degraded, the piercing strength and pinhole resistanceare lowered and therefore, it is not preferable. If the TD stretchingratio exceeds 6.0 times, the characteristics under a low humidity and ahigh humidity are significantly fluctuated and therefore, it is notpreferable. The TD stretching ratio is more preferably 3.0 to 5.0 times.In the invention, the stretching ratio on the basis of area ispreferably in a range of 6 to 25 times and more preferably in a range of9 to 22 times. If it is less than 6 times, no sufficient in-planeorientation can be obtained and the mechanical characteristics aredegraded and therefore, it is not preferable. If it exceeds 25 times,the shrinkage stress is increased and boiling stress is worsened andtherefore, it is not preferable.

(Film Characteristics-Elastic Modulus in MD Direction)

The biaxially stretched polyamide resin film of the invention ispreferable to have an elastic modulus in the longitudinal direction (MD)in a range of 1.7 to 3.5 Gpa at a relative humidity of 35%. A polyamideresin film containing no layered compound shows high elongation and highductility under a high humidity and contrarily shows low elongation andtends to be brittle under a low humidity. To increase the elasticmodulus in the MD direction, it is needed to heighten the stretchingratio not only in the MD direction but also in the TD direction and thusthere is a limit also in the stretching conditions. The biaxiallystretched polyamide resin film described in the invention is enabled tokeep the ductility and suppress the lowering of the elastic modulus at ahigh humidity and improve the elastic modulus and elongation at a lowhumidity. If the elastic modulus in MD is less than 1.7 GPa, theimprovement effect is slight and if it exceeds 3.5 GPa, it becomesdifficult to keep the balance with other characteristics and therefore,it is not preferable.

(Film Characteristics-Heat Shrinkage Ratio)

The biaxially stretched polyamide resin film of the invention ispreferable to have a heat shrinkage ratio at 160° C. for 10 minutes in arange of −3 to 3% in both of the lengthwise direction and transversedirection. In order to make the heat shrinkage ratio close to zero, itis preferable to optimize stretching conditions and thermal fixationcondition as well as to optimize the thickness of the layer. Forimprovement of the stretching property, it is advantageous that thethickness of each layer is thin; however if the layer is too thin, theheat shrinkage ratio cannot be lowered by thermal fixation andtherefore, the layer structure is preferable to be determined inaccordance with the aimed heat shrinkage ratio. To satisfy both of theheat shrinkage ratio and the stretching property all together, thethickness of each layer before stretching is preferably in a range of 1to 30 μm and more preferably in a range of 2 to 20 μm. The lower limitof the heat shrinkage ratio is more preferably 0% or higher and evenmore preferably 0.1% or higher. The upper limit of the heat shrinkageratio is more preferably 3.0% or lower and even more preferably 2.5% orlower.

(Film Characteristics-Pinhole Resistance)

The biaxially stretched film in the invention is excellent in thepinhole resistance and the number of pinholes after 1000 times GelboFlex test at 23° C. is preferably 0 to 30. The pinhole resistance ismainly affected by stretching conditions and particularly, it ispreferable that the temperature at the time of TD stretching isincreased not so high. In the case the TD stretching property isinferior, it is sometimes required to increase the temperature; howeverif the stretching temperature is increased too high beyond the lowtemperature crystallization temperature, partial crystallization ispromoted without progression of sufficient stretching and thicknessunevenness and pinholes tend to be formed easily in fine regions. Also,the pinholes are easy to be formed in the obtained film. With respect tothe TD stretching temperature, concretely, it is preferably 155° C. orlower. If it exceeds 155° C., the film tends to become brittle and thepinhole resistance is worsened and therefore, it is not preferable.

(Film Characteristics-Dimensional Change Ratio and Oxygen Permeability)

The biaxially stretched polyamide resin film in the invention ispreferable to have a dimensional change ratio in both of the lengthwiseand transverse directions in a range of 0.1 to 1.0% in the case 25° C.and relative humidity of 35% is changed to 25° C. and relative humidityof 85%. The heat shrinkage ratio and the hygroscopic dimensional changeratio in the width direction can be slightly adjusted in accordance ofthe relaxation ratio in the width direction at the time of thermalfixation; however they are essential issues in the lengthwise directionand particularly in the successive biaxial stretching, it is verydifficult to lower the hygroscopic dimensional change ratio in the caseof taking the balance with other characteristics into consideration. Itis pointed out that a conventional polyamide resin tends to easily causethe dimensional change because of disconnection of hydrogen bonds formedby the amide groups among the molecular chains by water; however thepolyamide resin in which the layered compound is evenly dispersedsuppressed the effect of water due to the interaction of the layeredcompound and the amide groups in the molecular chains and it can beassumed that the hygroscopic dimensional change can be suppressed byusing them; however, since conventionally there has been no properstretching method, it is not actually achieved. It is made possible toprovide highly advanced dimensional stability at the time of moistureabsorption by stretching the sheet with a multilayer structure in theinvention.

The biaxially stretched polyamide resin film in the invention containsthe layered compound oriented in the plane and is excellent in barrierproperty and has oxygen permeability in conversion into 15 μm preferablyin a range of 5 to 20 cc/m²/day/atm. The upper limit of the oxygenpermeability is preferably 19 cc/m²/day/atm or lower and more preferably18 cc/m²/day/atm or lower. Since the oxygen barrier property depends onthe addition amount of the layered compound in the polyamide resin (X)and (Y), the addition amount of the layered compound is preferably in arange of 2 to 20 wt. % in the entire film. If it is less than 2 wt. %,the effect of the barrier property is slight and if it exceeds 20 wt. %,the effect of barrier property improvement is saturated and it is noteconomical.

The biaxially stretched polyamide resin film of the invention may besubjected to corona treatment, coating treatment, or flame treatment toimprove the adhesiveness and wettability in accordance with use. Withrespect to the coating treatment, an in-line coating method ofstretching a coated product during film formation is one of preferableembodiments. The biaxially stretched polyamide resin film of theinvention is generally further processed by printing, deposition,lamination, etc. in accordance with use.

The biaxially stretched polyamide resin film of the invention maycontain arbitrarily a hydrolysis resistant improver, an antioxidant, acoloring agent (a pigment, a dye), an antistatic agent, a conductiveagent, a flame retardant, a reinforcing agent, an organic lubricant, anucleating agent, a release agent, a plasticizer, an adhesive aid, apressure-sensitive adhesive, etc.

Next, the second invention will be described in detail.

With respect to lowering of the shrinkage stress at the time of boiling,besides increase of the heat resistance of a resin, it is effective tolower the shrinkage stress. The inventors of the invention have foundthat it is enabled to lower the stretching stress by lowering theentanglement density of molecular chains in the thickness direction bymultilayer formation and thereby improving the deformation easiness ofthe molecular chains and as a result the shrinkage stress can be loweredin spite of in-plane orientation same as that of a film with a monolayerstructure. Also, the inventors have found that these methods can lowerthe bowing and that it is made possible to provide a production methodwith high industrial applicability and a stretched film with excellentcharacteristics.

(Polyamide Resin)

A polyamide resin to be used in the invention is not particularlylimited and may include a ring-opening polymers of cyclic lactams,condensates of diamines and dicarboxylic acids, and self condensates ofaminoacids and examples are not particularly limited, but are nylon 6,nylon 7, nylon 66, nylon 11, nylon 12, nylon 4, nylon 46, nylon 69,nylon 612, and m-xylylene diamine type nylon. Copolymer type polyamideresins may be also used. Concretely, examples are aromatic polyamideresins such as nylon 6 and nylon 66 copolymerized withm-xylylenediamine, nylon 6T, nylon 6I, nylon 6/6T copolymers, nylon 6/6Icopolymers, nylon 6/polyalkylene glycol resins, nylon 11/polyalkyleneglycol resins, nylon 12/polyalkylene glycol resins, nylon 6/MXD 6copolymers and also usable resins are those obtained by copolymerizationof other components with these resins and preferable examples are nylon6, nylon 66, m-xylylenediamine type nylon. Particularly, the gaspermeability is remarkably decreased by laminating a few layers of am-xylylenediamine type nylon resin and thus it is one of preferableembodiments of the invention.

Further, besides polyamide resin described below, other resins andadditives may be added to these resins for use. Moreover, in terms ofthe economy, one of preferable embodiments is use of a recovered filmproduced by the invention for a part or all of a polyamide resin. Usableexamples of other resins are conventionally known resins such aspolyester resins, polyurethane resins, acrylic resins, polycarbonateresins, polyolefin resins, polyester elastomer resins, and polyamideelastomer resins and not limited thereto.

With respect to the slipping property, various kinds of lubricants maybe added to provide surface roughness and both organic type lubricantsand inorganic type lubricants can be used. Although not particularlylimited in the invention, sufficient slipping property can be providedwithout addition of these lubricants in the invention and the lubricanttype to be added and the addition amount should be determined taking thevarious kinds of characteristics. In the case of an inorganic typelubricant, the particle diameter is preferably 0.5 μm or larger and morepreferably 1 μm or larger. The addition amount is preferably in a rangeof 100 to 5000 ppm in the layer forming the surface layer. If it is lessthan 100 ppm, the addition effect is slight and if it exceeds 5000 ppm,the effect is saturated and therefore, it is not economical.

(Polyamide Resin Containing Layered Compound Evenly Dispersed Therein)

In the invention, besides a common polyamide resin, a polyamide resincontaining layered compound evenly dispersed therein, described below,can be used. In this case, the heat resistance, barrier property andhygroscopic strain of a resin can be improved and it is one ofpreferable methods.

The polyamide resin containing layered compound evenly dispersed thereinis commonly called as nano-composite nylon. The layered compound isevenly dispersed and preferably contains no coarse material larger than2 μm thickness of the layered compound. In the case the coarse materiallarger than 2 μm is contained, the transparency is lowered and thestretching property is deteriorated and therefore, it is not preferable.

Examples of the layered compound are not limited to, but are layeredcompounds such as swelling mica, clay, montmorillonite, smectite,hydrotalcite, etc., which are usable regardless of being inorganic andorganic. The form of the layered compound is not particularly limited;however, those having an average length of the longer diameter of 0.01to 50 μm, preferably 0.03 to 20 μm, even more preferably 0.05 to 12 μmand an aspect ratio of 5 to 5000, preferably 10 to 5000 are preferablyused. The addition amount of an inorganic layered compound with respectto the above-mentioned polyamide resin is preferably 0.3 to 10 wt. %. Aninorganic layered compound is sometimes added in form of an organicallytreated layered compound and the addition amount and the content(addition amount) of the inorganic material according to the weightresidue described below are not necessarily correspond with each other.Further, if a method for measuring it from the residue weight asdescribed below is employed, a small amount of an inorganic materialother than the inorganic layered compound is added in some cases and inthe invention, it is calculated as the content of the inorganic materialincluding the layered compound. The content of the inorganic materialincluding the layered compound is a value calculated by subtracting theash from the residue weight measured by a thermogravimetric analyzer(TGA) and concretely, it is calculated by measuring the residue weightafter increasing the temperature of a resin containing a layeredcompound from room temperature to 550° C. and thereafter subtracting thevalue of resin ash therefrom. In Example 1, the inorganic content can bemeasured to be 2.6% by subtracting 1.8% of residue weight derived fromthe resin from 4.4% of residue weight by TGA. Also, the ratio of anorganic treatment agent in the layered compound is separately measuredby TGA, and calculation using the numeral value can be employed.

The lower limit of the content of the layered compound is morepreferably 0.3%, furthermore preferably 0.5%, and most preferably 0.7%.If it is less than 1.0%, the effect of the layered compound addition isslight in terms of the slight effect on the dimensional stability andmechanical characteristics and thus it is not preferable. Also, thestatic friction coefficient may be increased and the slipping propertymay be worsened.

The upper limit is more preferably 10% or less and furthermorepreferably 8% or less. If it is more than 10%, the effect on thedimensional stability and mechanical characteristics is saturated and itis not economical and the fluidity at the time of melting is lowered andthus it is not preferable. Further, the surface roughness becomesunnecessarily significant and the haze may be lowered.

Common layered compounds may be used and organically treatedcommercialized products preferably usable in a monomer insertionpolymerization method described below are Cloisite produced by SouthernClay Products Inc., Somasif and Lucentite produced by Co-op ChemicalCo., Ltd., and S-Ben produced by Hojun Yoko Co., Ltd.

The layered compound is preferable to be evenly dispersed in theabove-mentioned polyamide resin in the invention and its productionmethod can be exemplified as follows.

1. Interlayer insertion method

1) monomer insertion polymerization method

2) polymer insertion method

3) lower organic molecule insertion (organic swelling) kneading method

2. In-situ method: In-situ filler formation method (sol-gel method)3. Ultrafine particle direct dispersion method, etc.

Commercialized materials may include Cress Alon NF 3040 and NF 3020produced by Nanopolymer Composite Corp.; NCH 1015C2 produced by UbeIndustries Ltd.; and Imperm 103 and Imperm 105 produced by Nanocor, Inc.In order to heighten the dispersibility of the layered compound forsuppressing formation of coarse matter of the layered compound containedin the polyamide resin, it is preferable to treat the layered compoundwith various kinds of organic treatment agents; however to avoid anadverse effect of thermal decomposition of a treatment agent at the timeof melt molding, those obtained by using a low molecular weight compoundwith high heat stability or by a method such as the monomer insertionpolymerization method in which a low molecular weight compound is notused are preferable. With respect to the heat stability, a treatedlayered compound having a 5% weight loss temperature of 150° C. orhigher is preferable. TGA or the like can be employed for themeasurement. In the case of a compound with inferior heat stability,foams may be formed in the film or coloring may be caused and therefore,it is not preferable (reference to “Challenging nano-technologicalmaterials: Polymer nano-composites in widened application developments”,Sumitomo Bakelite-Tsutsunaka Techno Co., Ltd.)

The layered compound is preferably in-plane oriented in a film to beobtained for exhibiting characteristics. The in-plane orientation can beconfirmed by observing a cross section by a transmission electronmicroscope or a scanning electronic microscope.

(Film Formation Method)

The biaxially stretched multilayer polyamide resin film of the inventioncan be produced by a common method and obtained by stretching amultilayer un-stretched sheet obtained by various methods in the sameconditions as those in a common case, and the thickness of each layerand the stretching conditions are controlled to give a prescribedin-plane orientation, so that a film with little boiling strain andexcellent in various characteristics can be obtained. The effect of themultilayer formation is based on that the stretching stress andconsequently shrinkage stress at the time of boiling are lowered bydecreasing the entanglement of molecular chains in the thicknessdirection and as a result, bowing is lessened and the boiling strain isdecreased.

Hereinafter, the system of addition of a layered inorganic compound willbe described. In stretching of a resin containing a layered inorganiccompound, problems in the case of stretching by employing successivebiaxial stretching in lengthwise-transverse order, which is generallyadvantageous in terms of economy, are following three points: (1) in thestretching in the lengthwise direction (hereinafter, abbreviated as MD),crystallization proceeds due to the heat at the time of stretching andthe stretching property in the transverse direction (hereinafter,abbreviated as TD) is lost after uniaxial stretching; (2) breakingoccurs at the time of stretching in TD; and (3) breaking occurs at thetime of thermal fixation after stretching in TD. With respect to (1),when the MD stretching conditions in which the TD stretching is possibleand the MD stretching conditions in which the TD stretching isimpossible are put in order, it is found that the refractive index inthe width direction (refractive index in the y-axis, hereinafter,abbreviated as Ny) of a uniaxially stretched sheet after the MDstretching differs from each other. Concretely, it is found that Ny of auniaxially stretched sheet which is TD-stretchable becomes low after theMD stretching, whereas Ny of a uniaxially stretched sheet which is notTD-stretchable (that is, whitened or broken at the time of TDstretching) is scarcely changed or not at all changed after the MDstretching. It is found that in stretching of a common polyamide resin,Ny after the MD stretching becomes low simultaneously with occurrence ofneck-in in the width direction at the time of the MD stretching and onthe other hand, in the case a layered compound is added thereto, neck-inoccurs, but Ny tends to be difficult to be low due to the interaction ofthe layered compound and polyamide resin molecules. The phenomenon issupposedly attributed to as follows: since the molecular chains of afilm before stretching are oriented at random in MD and TD directions,force is generated also in the TD direction at the time of stretchingmolecular chains in the MD direction by the MD stretching, and the forceapplied also in the TD direction can be released by the neck-in in theTD direction in the case of stretching of a common polyamide resin; andon the other hand, in the case of the polyamide resin containing alayered compound, since the molecular chains are cramped by the layeredcompound, the force in the TD direction cannot be released and themolecular chains are put in the state as if they are pulled also in theTD direction, and also the layered compound is rotated at the time ofthe MD stretching and therefore, molecules are pulled also in directionsother than the MD direction. That is, the in-plane orientation isalready in a high state after the MD stretching. Therefore, it issupposed that the stretching stress at the time of successively carryingout the TD stretching becomes high and breaking is caused.

As a method for solving this problem, stretching conditions in which Nybecomes small after the MD stretching are employed to make the TDstretching at a high ratio possible without causing breaking in the TDstretching successively carried out thereafter and thus it is madepossible to produce a film of the invention in industrial scale.

In the case Ny(A) is defined as the refractive index in the widthdirection before lengthwise stretching and Ny(B) is defined as therefractive index in the width direction after lengthwise stretching,Ny(A)−Ny(B) is preferably 0.001 or higher. It is more preferably 0.002or higher and most preferably 0.003 or higher.

As a method for lowering Ny after uniaxial stretching, a method ofconsiderably lowering the MD stretching rate can be employed; however,besides, it is made possible to exhibit a similar effect bymulti-layering an un-stretched sheet after melt extrusion. That is, theentanglement density of molecular chains is lowered in the thicknessdirection by multi-layering and thus the deformability of the molecularchains is improved and Ny can be lowered and as a result, increase ofin-plane orientation at the time of the MD stretching can be suppressedand the TD stretching property can be improved. The inventors have foundthat biaxial stretching property can be improved by these methods andhave completed a production method with high industrial applicabilityand a stretched film with excellent characteristics.

(Construction of Film)

The biaxially stretched multilayer polyamide resin film of the inventioncan be obtained essentially by stretching an un-stretched multilayerpolyamide resin sheet having 8 layers or more in total.

In the invention, the number of layers is preferably at least not lessthan 8 layers and more preferably not less than 16 layers. If it is lessthan 8 layers, the effect of lowering the entanglement density in thethickness direction is slight and the effect of lowering the boilingstrain is slight and therefore, it is not preferable. The conditions ofthe number of the layers is preferably not more than 10000 layers andmore preferably 5000 layers. If it exceeds 10000 layers, the heatshrinkage ratio after the thermal fixation is not lowered and therefore,it is not preferable.

The thickness of each layer before stretching is preferably 10 nm to 30μm and more preferably 100 nm to 10 μm. If it is thinner than 10 nm, theheat shrinkage ratio after the thermal fixation is not lowered andtherefore, it is not preferable. If it exceeds 30 μm, the effect oflowering the entanglement density in the thickness direction is slightand the effect of lowering the boiling strain is slight and therefore,it is not preferable.

With respect to the biaxially stretched multilayer polyamide resin filmof the invention, 80% or more layers as the ratio of the number oflayers are preferable to contain the same resin composition. If it isless than 80%, the effect of the shrinkage stress derived from anotherresin layer becomes significant, resulting in diminution of the effectof decrease of the shrinkage stress and diminution of the effect ofdecrease of the boil strain and therefore, it is not preferable.

(Laminating Method)

At the time of multi-layering of the above-mentioned polyamide resin inthe invention, besides laminating different kinds of resin as employedcommonly, it is possible to layer the same kind of resin. Herein,although it seems to be difficult to find the physical meaning ofmulti-layering with the same kind of resin by a method described below;however, in an actual system, an interface of layers does not disappeareven in the case of the same resin is laminated by melt extrusion at thesame temperature and it exists even after stretching. It is the same asthat a welded line of an injection-molded product is difficult to beeliminated. As described, even the same type resin is used, multilayerstate is maintained and the entanglement of molecules in the thicknessdirection can be suppressed and kept low. A method for confirming theexistence of an interface of layers at the time of laminating of thesame kind of resin by melt extrusion may be a method of cooling a samplewith ice or liquefied nitrogen, producing a cross section by cutting thesample with a razor or the like thereafter, immersing the obtainedsample in a solvent such as acetone, and observing the cross sectionwith a microscope.

A polyamide resin and a resin composition composing other layers basedon necessity are supplied separately to respective extruders andextruded at a temperature higher than melting temperature and themelting temperature is preferably lower by 5° C. than the decompositionstarting temperature. Further, in the case of using a resin containingthe layered compound, to suppress cracking of the layered compound inthe resin, the melting conditions and melting temperature have to be setcarefully. In the case of a polyamide resin with a high molecularweight, the layered compound is cracked if melting at such a lowtemperature as not higher than melting point +10° C. is carried out, andthe aspect ratio becomes smaller than that in the initial state and thusthe effect of use of the layered compound with a high aspect ratio isdiminished and therefore, it is preferable to carry out melting at ahigh temperature in a range with no problem in terms of heat stability.

A polyamide resin and a resin composition composing other layers basedon necessity are laminated by various kinds of methods and a feed-blockmethod and a multi-manifold method can be employed. In the case of thefeed-block method, at the time of widening the width to the die widthafter laminating, if the melt viscosity difference between laminatedlayers and the temperature difference at the time of laminating aresignificant, they result in laminating unevenness, deterioration of theappearance, and unevenness of the thickness and therefore, they shouldbe carefully controlled at the time of production. For suppression ofoccurrence of unevenness, it is preferable to control the melt viscosityat the time of extrusion by (1) lowering the temperature and (2) addingvarious kinds of additives such as polyfunctional epoxy compounds,isocyanate compounds, carbodiimide compounds, etc.

In the invention, promotion of orientation in the plane of the layeredcompound by the shear force at the time of laminating is also effectiveto suppress the breaking by convergence of the stress to the tip end ofthe layered compound at the time of stretching. As a method suitable forsuch a purpose, laminating by a feed block method and a static mixermethod is preferable.

The melting temperature difference between respective layers at the timeof laminating of the polyamide resin is 70° C. or lower, preferably 50°C. or lower, and more preferably 30° C. or lower. The melt viscositydifference of resins between layers is adjusted to be within 30 times,preferably within 20 times, and more preferably within 10 times at theestimated shear rate in a die, so that the appearance control at thetime of laminating and unevenness suppression can be made possible. Forthe adjustment of the melt viscosity, addition of the above-mentionedpolyfunctional compounds can be employed. The static mixer temperatureor feed block temperature at the time of laminating is in a range of 150to 330° C., preferably 170 to 220° C., and more preferably 180 to 300°C. Since the laminating state becomes better as the viscosity is higherat the time of laminating, the feed block temperature and static mixertemperature is more preferable as being lower; however if the feed blocktemperature and static mixer temperature is too low, the melt viscositybecomes too high and the load on the extruder becomes too high andtherefore, it is not preferable. If the temperature is high, theviscosity is too low and laminating unevenness occurs and therefore, itis not preferable.

Further, laminating is possible by a multi-manifold method and theabove-mentioned problem of laminating unevenness is hardly caused;however, in the case of laminating a layer with a melt viscositydifference, there occurs a problem of a turning-around failure of theresins in the respective layers in the end parts and unevenness of thelaminating ratio in the end parts in terms of productivity and also inthis case, it is preferable to control the melt viscosity difference.

For the die temperature, it is the same as described above and it is ina range of 150 to 300° C., preferably 170 to 290° C., and morepreferably 180 to 285° C. If the temperature becomes too low, the meltviscosity becomes too high and the surface roughening occurs to resultin appearance deterioration. If the temperature becomes too high,thermal decomposition of the resin is caused and in addition to that, asdescribed, the melt viscosity difference becomes wide and unevenness iscaused and particularly, unevenness with small pitches is caused andtherefore, it is not preferable.

(Stretching Method)

For a biaxially stretched multilayer polyamide resin film of theinvention, an un-stretched sheet extruded by melt extrusion from a T diecan be stretched by successive biaxial stretching and simultaneousbiaxial stretching, and in addition, a method such as a tubular mannercan be employed; however to carry out sufficient orientation, a methodusing a biaxial stretching apparatus is preferable. In terms of thecharacteristics and economy, a preferable method is a method ofstretching in the lengthwise method by a roll type stretching apparatusand thereafter stretching in the transverse direction by a tenter typestretching apparatus (successive biaxial stretching method). Further,with respect to the MD stretching, since it is preferable to lower MDorientation at the time of the MD stretching for lessening bowing, it ispreferable to employ multi-step MD stretching.

It is preferable to obtain the film by stretching a substantiallyun-oriented polyamide resin sheet obtained by melt extrusion from a Tdie 2.5 to 10 times as large in the lengthwise direction at atemperature equal to or higher than the glass transition temperature Tg°C. of the polyamide resin and not higher than 150° C.; thereafterstretching the lengthwise stretched film 3.0 to 10 times as large at atemperature of not lower than 50° C. and not higher than 155° C., andsuccessively, thermally fixing the biaxially stretched polyamide resinfilm in a temperature range of 150 to 250° C.

The heating crystallization temperature can be measured by increasingthe temperature of a sample resin which has been quenched after meltingby DSC.

In the MD stretching, if the temperature of the film is lower than theglass transition temperature Tg° C. of the polyamide, problems ofbreaking and unevenness of the thickness due to the orientedcrystallization by stretching occurs. On the other hand, if the filmtemperature exceeds 150° C., breaking is caused due to thecrystallization by heat and therefore, it is not proper. Further, thestretching ratio of the MD stretching in the invention is preferably 2.5to 5.0 times and more preferably 2.8 to 4.5 times. If the stretchingratio of the MD stretching is less than 2.5 times, problems of qualityinferiority such as unevenness of the thickness and insufficientstrength in the lengthwise direction are caused and if it exceeds 5times, the effect for decreasing the boiling strain is diminished andtherefore, it is not preferable. The MD stretching may be one-step ormulti-step process.

Further, in the case the film temperature in the TD stretching is alower than 50° C., the TD stretching property is bad and breaking occursand unevenness of the thickness in the TD direction attributed to theneck stretching becomes significant and therefore, it is not preferable.On the other hand, in the case the film temperature is a hightemperature beyond 155° C., unevenness of the thickness becomessignificant and therefore, it is not preferable. Further, if the TDstretching ratio is less than 1.1 times, unevenness of the thickness inthe TD direction becomes significant and it is not preferable and thestrength in the TD direction is lowered and in addition, the in-planeorientation becomes inferior, which results in worsening of thecharacteristics not only in the TD direction but also in the MDdirection and therefore, it is not preferable. The stretching ratio istherefore preferably 3 times or more. On the other hand, if the TDstretching ratio is a high ratio beyond 10 times, practical stretchingis difficult. The TD stretching ratio is preferably 3.0 to 5.0 times.

The stretching ratio based on the area at the time of producing thebiaxially stretched multilayer polyamide resin film of the invention ispreferably in a range of 6 to 25 times and more preferably in a range of9 to 22 times. If it is lower than 6 times, sufficient in-planeorientation cannot be done and the mechanical characteristics aredegraded and therefore, it is not preferable. On the other hand, if itexceeds 25 times, the shrinkage stress becomes significant and theboiling strain cannot be diminished and therefore, it is not preferable.

With respect to the stretching temperature, stretching at a lowtemperature is preferable in terms of sufficient exhibition of theaddition effect of the layered silicate, unevenness of thickness of thefilm, and Gelbo Flex resistance. A preferable condition may bestretching at a film temperature of 155° C. or lower at the time ofstretching.

(Thermal Fixation)

In the case a thermal fixation temperature is a low temperature lowerthan 150° C., the thermal fixation effect of the film by heat is slightand therefore, it is improper. On the other hand, in the case of a hightemperature exceeding 250° C., appearance degradation due to whiteningattributed to thermal crystallization of the polyamide and decrease ofthe mechanical strength are caused and therefore, it is improper.

In addition, in the system containing the layered compound, the densityincrease due to crystallization in the thermal fixation after the TDstretching and the accompanying volume shrinkage are caused, and in thecase of the resin containing the layered compound, the stress to begenerated is remarkably high and therefore, stress is applied in the MDdirection by sharp heating and it sometimes results in breaking.Therefore, as a heating method at the time of thermal fixation, it ispreferable to increase the heat quantity step by step and thusgeneration of acute shrinkage stress is suppressed. A concrete method isexemplified as a method of gradually increasing the temperature orincreasing the air blow amount toward the surrounding of the outlet fromthe surrounding of the inlet of a thermal fixation zone and ispreferably a method of gradually increasing the air blow amount in termsof the thermal shrinkage ratio after stretching and thermal fixation.

Further, with respect to the relaxation treatment, taking the balancewith the heat shrinkage ratio into consideration, it is preferable todetermine the relaxation ratio. In the invention, since the dimensionalstability with respect to humidity in the lengthwise direction is small,the relaxation ratio is preferably in a range of 0 to 5%. If it exceeds5%, the effect on decrease of the heat shrinkage ratio in the widthdirection is slight and therefore, it is not preferable.

(In-Plane Orientation)

After the biaxial stretching, thermal fixation, and relaxationtreatment, the biaxially stretched multilayer polyamide resin film ofthe invention has an in-plane orientation (ΔP) of preferably 0.057 to0.07. The in-plane orientation can be measured by measuringbirefringence with a refractive index meter and carrying out calculationaccording to the following expression:

ΔP=(Nx+Ny)/2−Nz,

wherein Nx is the refractive index in the longitudinal direction; Ny isthe refractive index in the width direction; and Nz is the refractiveindex in the thickness direction.

The in-plane orientation can be increased by increasing the biaxialstretching ratio, particularly the TD stretching ratio and if thein-plane orientation is less than 0.057, the mechanical strength such asthe piercing strength of the film is lowered and therefore, it is notpreferable. Further, if the in-plane orientation exceeds 0.07, theproductivity is lowered and therefore, it is not preferable.

(Boiling Strain)

The boiling strain of the biaxially stretched multilayer polyamide resinfilm in the invention is preferably 0.1 to 2.0%. The boiling strain iscaused by fixation of the end parts in relation to the shrinkage in thecenter part at the time of TD stretching and it is considerably notablein the end parts in the width direction of the film and if the shrinkagedegree at the times of boiling treatment is lowered, the boiling strainis diminished. To lower the shrinkage degree, besides the stretchingstress is lowered by multilayer formation, which is a point of theinvention, setting of the stretching conditions is also important;however if the conditions are not considerably out of conventionalconditions for stretching a polyamide resin, it can be sufficientlylowered. If the boiling strain exceeds 2.0%, curling is notable andtherefore, it is not preferable.

(Film Characteristics-Haze)

The haze of the biaxially stretched multilayer polyamide resin film inthe invention is preferably in a range of 1.0 to 20%. If the haze at thetime of stretching is 1.0% or lower, stable production becomes difficultand therefore, it is not preferable. If haze exceeds 20%, it becomesdifficult to see contents at the time of use and additionally, thedesign property is deteriorated and therefore, it is not preferable.

The haze of the system containing the layered compound of the inventionis the total derived from the resin, derived from the inorganic layeredcompound, and derived from voids formed by separation of the resin fromthe inorganic layered compound surface at the time of stretching and itis preferable to decrease particularly haze derived from the voids andfor that, the stretching conditions are preferable to be set carefully.Concretely, in the case the MD temperature is too low, the haze isincreased due to voids formation and therefore, it is not preferable.Also, in the case the TD temperature is too high, haze increase isobserved due to crystallization and therefore, it is not preferable. Apreferable temperature range is as described above and it can beadjusted with reference to these facts. Further, it can be adjusted inaccordance with the size and type of the layered compound. For example,not only use of the layered compound with a size smaller than thewavelength of visible light makes the haze small but also use of thelayered compound with a refractive index close to that of the resinmakes the haze small.

(Film Characteristics-Pinhole Resistance)

The biaxially stretched multilayer polyamide resin film in the inventionis excellent in the pinhole resistance and the number of pinholes after1000 times Gelbo Flex test at 23° C. is preferably 0 to 30. The pinholeresistance is mainly affected by stretching conditions and particularly,it is preferable that the temperature at the time of TD stretching isincreased not so high. In the case the TD stretching property isinferior, it is sometimes required to increase the temperature; howeverif the stretching temperature is increased too high beyond the lowtemperature crystallization temperature, partial crystallization ispromoted without progression of sufficient stretching and thicknessunevenness and pinholes tend to be formed easily in fine regions. Also,the pinholes are easy to be formed in the obtained film.

With respect to the TD stretching temperature, concretely, it ispreferably 155° C. or lower. If it exceeds 155° C., the film tends tobecome brittle and the pinhole resistance is worsened and therefore, itis not preferable.

(Film Characteristics-Equilibrium Moisture Content)

The equilibrium moisture content of the polyamide resin film in theinvention is preferably in a range of 3.5 to 10%. The equilibriummoisture content of a common biaxially stretched film of a polyamideresin is about 3% and the film of the invention is preferably higherthan that. Among commonly known layered compounds, most commonly usedmontmorillonite and smectite are generally used as a thickener forincreasing the viscosity of an aqueous solution. As being assumed fromthat, they have characteristics of taking water in inter-layers, beingswollen easily, and absorbing a large quantity of water. If thesecompounds are merely added to a resin, montmorillonite absorbs a largequantity of water. Therefore, the equilibrium moisture content in theresin composition becomes higher and the characteristics become highlymoisture-dependent. According to the invention, since the layeredcompound is highly in-plane orientated, and also, even if the additionamount is so high as to give the equilibrium moisture content of 3.5% orhigher, the moisture-dependency of the characteristics can be suppressedby biaxial stretching of the matrix polyamide resin at a high ratio andfurther carrying out orientation crystallization. If the equilibriummoisture content is less than 3.5%, the effect of the layered compoundaddition is slight and if it exceeds 10%, the addition amount is excessand preferable characteristics cannot be obtained.

(Film Characteristics-Gas Barrier Property)

In the invention, the multilayer film containing the layered compound isexcellent in the barrier property since the layered compound is orientedin the plane, and it is preferable that the oxygen permeability inconversion into 15 μm is in a range of 5 to 20 cc/m²/day/atm. The upperlimit of the oxygen permeability is preferably 19 cc/m²/day/atm or lowerand more preferably 18 cc/m²/day/atm or lower. The oxygen barrierproperty depends on the in-plane orientation degree of the layeredcompound in the polyamide resin and the addition amount, and apreferable addition amount of the layered compound in terms of theoxygen barrier property is in a range of 0.3 to 10 wt. % with respect tothe entire film. If it is less than 0.3 wt. %, the effect of the barrierproperty is slight, and if it exceeds 10 wt. %, the balance with thecharacteristics such as the boiling strain is worsened and therefore, itis not preferable. Further, aiming to further heighten the gas barrierproperty, it is preferable to add a resin with a high barrier propertyand to laminate a resin layer with a high barrier property. Examples ofthe resin with a high barrier property are m-xylylenediamine type nylon(MXD6), polyvinyl alcohol, polyglycolic acid, etc. The addition amountand the laminating amount of these compounds is preferably 1 to 20%. Ifit is less than 1%, the effect of improving the barrier property isslight and if it exceeds 20%, the added barrier resin and the stretchingproperty cannot be well balanced and therefore, it is not preferable.

(Film Characteristics-Heat Shrinkage Ratio)

The biaxially stretched multilayer polyamide resin film of the inventionis preferable to have a heat shrinkage ratio at 160° C. for 10 minutesin a range of −0.5 to 1.5% in both of the lengthwise direction andtransverse direction. In order to make the heat shrinkage ratio close tozero, it is preferable to optimize stretching conditions and thermalfixation condition as well as to optimize the thickness of the layer.For improvement of the stretching property, it is advantageous that thethickness of each layer is thin; however if the layer is too thin, theheat shrinkage ratio cannot be lowered by thermal fixation andtherefore, the layer structure is preferable to be determined inaccordance with the aimed heat shrinkage ratio. To satisfy both of theheat shrinkage ratio and the stretching property all together, thethickness of each layer before stretching is preferably in a range of 1to 30 μm and more preferably in a range of 2 to 20 μm. The lower limitof the heat shrinkage ratio is more preferably 0% or higher and evenmore preferably 0.1% or higher. The upper limit is preferably 1.5% orlower and more preferably 1.3% or lower.

The biaxially stretched multilayer polyamide resin film of the inventionmay be subjected to corona treatment, coating treatment, or flametreatment to improve the adhesiveness and wettability in accordance withuse. With respect to the coating treatment, an in-line coating method ofstretching a coated product during film formation is one of preferableembodiments. The biaxially stretched multilayer polyamide resin film ofthe invention is generally further processed by printing, deposition,lamination, etc. in accordance with use.

The biaxially stretched polyamide resin film of the invention maycontain arbitrarily a hydrolysis resistant improver, an antioxidant, acoloring agent (a pigment, a dye), an antistatic agent, a conductiveagent, a flame retardant, a reinforcing agent, a filler, an inorganiclubricant, an organic lubricant, a nucleating agent, a release agent, aplasticizer, an adhesive aid, a pressure-sensitive adhesive, etc.

EXAMPLES

Next, the invention will be described more in detail with reference toExamples; however the invention is not to be considered as being limitedby these Examples, but is only limited by the scope of the appendedclaims. Measurement methods employed in the invention will be describedbelow.

(1) Haze

Haze was measured at different 3 points of each sample by using a hazemeter (NDH 2000, produced by Nippon Denshoku Industries Co., Ltd.)according to a method of JIS K7105 and the average value was employed.

(2) Measurement of Glass Transition Temperature (Tg) and Measurement ofLow Temperature Crystallization Temperature (Tc)

An un-oriented polyamide resin sheet was frozen in liquefied nitrogenand after thawing under reduced pressure, these temperatures weremeasured at heating rate of 20° C./min by using DSC produced by SeikoInstruments Inc.

(3) Addition Amount of Inorganic Material Including Layered Compound(Residue Weight)

The weight of residue was measured by using TGA manufactured by TAInstruments after 0.1 g of each sample was heated to 500° C. at aheating rate of 20° C./min under nitrogen flow.

(4) Surface Roughness (Sa)

Small pieces were cut off from arbitrary 3 parts of each film and dustor the like was carefully removed by a static elimination blower. Theheat adhesion layer surface of each piece was measured by a non-contactthree-dimensional shape measurement apparatus (Micromap 557 manufacturedby Micromap Corp.). For the optical system, a Millot type two beaminterference object lens (10 magnification) and a zoom lens (Body Tube;0.5 magnification) were used. Light was received by a ⅔ inch CCD camerausing a light source of 5600 angstrom. The measurement was carried outin WAVE mode, and the visual field of 1619 μm×1232 μm was processed as adigital image of 640×480 pixels. The image analysis was carried outusing an analysis software (Micromap 123, version 4.0) by detrending ina linear function mode. Accordingly, arithmetic average surfaceroughness for 5 visible fields of each front face and each rear face ofthree samples (total 30 visible fields) were measured and the averagevalue was defined as the surface roughness (Sa).

(5) Static Friction Coefficient

The static friction coefficient was measured by a friction coefficienttest method described in JIS K7125. Ten samples were cut off fromarbitrary 5 points of each film and both front and rear faces of thefilm were set face to face for measurement. The normal stress calculatedby the load applied to the sliding specimen was set to be 0.5 N/cm² andthe average value of 5 times measurement results was defined as thestatic friction coefficient. The measurement environments were 23° C.and 65% RH.

(6) Gloss

As the gloss, 85-degree mirror face gloss was measured using a specimenof a size of 100×100 mm according to JIS K8741 with a gloss meter (glossmeter model 1001 DP, produced by Nippon Denshoku Industries Co., Ltd.).The value was the average value of front and rear faces.

(7) Mechanical Characteristic (Elastic Modulus)

This is according to JIS K 7113. Specimens with a width of 10 mm and alength of 100 mm in the width direction and the longitudinal directionwere cut off from each film by a razor and used. After the specimenswere left in atmosphere of 23° C. and 35% RH for 12 hours, themeasurement was carried out in atmosphere of 23° C. and 35% RH and underconditions of chuck interval of 40 mm and tensile speed of 200 mm/min.The average value of 5 times measurement results was employed. AutographAG 5000 A manufactured by Shimadzu Corp. was used as a measurementapparatus. The high temperature MD elastic modulus was measured in anoven heated to a prescribed temperature under conditions of chuckinterval of 40 mm and tensile speed of 200 mm/min. The average value of5 times measurement results was employed.

(8) Dynamic Viscoelasticity Test

The measurement was carried out by a dynamic viscoelasticity measurementapparatus produced by I.T. Research Co., Ltd. under conditions ofmeasurement length of 30 mm, displacement of 0.25%, frequency of 10 Hz,and measurement environment temperature of 23° C. Each sample was cutoff in a size of length 40 mm×width 5 mm in parallel to the widthdirection of each film. The average value of two points was employed.Calculation of tan δ was carried out according to the followingexpression:

tan δ=(imaginary number of complex elastic modulus)/(real number ofcomplex elastic modulus).

(9) Pinhole Resistance (Flex Resistant Fatigue Test)

Flex resistant fatigue property was measured by the following methodusing a Gelbo Flex tester produced by Rigaku Kogyo Co., Ltd. A test wascarried out with a Gelbo Flex tester (produced by Rigaku Kogyo Co.,Ltd.). At first, each obtained film sample was attached in cylindricalform to a fixed head with a diameter of 8.89 cm (3.5 inch) and a movablehead with the same diameter and arranged in parallel at an interval of17.78 (7 inch) from the fixed head. The movement of the movable head wascontrolled by a shaft installed in the center of the movable head. Atfirst, while being twisted at 440°, the movable head was moved closer by8.89 cm (3.5 inch) to the fixed head and next further moved closer by6.35 cm (2.5 inch) by horizontal movement and thereafter, the movablehead was turned back to the former state by the inversion movement. Thiscycle was repeated 1000 times at 23° C., 60% RH, and a speed of 40times/min. After repeated 1000 times, the number of pinholes wasmeasured. The measurement of the number was carried out by the followingmethod. The film was put on filter paper (No. 50, Advantec) and fourcorners were fixed by Sellotape (registered trademark). Ink (Inkproduced by Pilot Corporation (product No. INK-350-Blue) dilutedfivefold with pure water) was applied to the test film and spread on oneface by a rubber roller. After excess ink was wiped out, the test filmwas removed and the number of points of the ink on the filter paper wascounted.

(10) Mechanical Characteristics (Maximum Point Stress, BreakingElongation)

This is according to JIS K 7113. Specimens with a width of 10 mm and alength of 100 mm in the width direction and the longitudinal directionwere cut off from each film by a razor and used. After the specimenswere left in atmosphere of 23° C. and 35% RH for 12 hours, themeasurement was carried out in atmosphere of 23° C. and 35% RH and underconditions of chuck interval of 40 mm and tensile speed of 200 mm/min.The average value of 5 times measurement results was employed. AutographAG 5000 A manufactured by Shimadzu Corp. was used as a measurementapparatus.

(11) Relative Viscosity

The relative viscosity was measured at 20° C. after 0.25 g of nylonresin was dissolved in 25 ml of 96% sulfuric acid solution.

(12) In-Plane Orientation of Layered Compound

With respect to a film obtained by stretching a nylon 6 resin in whichmontmorillonite was dispersed, the in-plane orientation ofmontmorillonite was measured. In the case of compounds other thanmontmorillonite, measurement could be carried out in the same manner.RINT 2500 Cu—Kα produced by Rigaku Corporation was used as the apparatusand the half width of the peak of (060) montmorillonite was measured byx-ray diffractometry with output of 40 kV and 200 mA. The in-planeorientation of the inorganic layered compound was calculated from thehalf width according to in-plane orientation=(180−half width)/180.

Herein, the half width of the peak of (060) of montmorillonite wasmeasured by the following method: (1) x-ray was led in the width (TD)direction to the film sample; (2) the sample was fixed at a position of0=31.4° to the incident x-ray and the detector was fixed at a positionof 2θ=62.8°; (3) x-ray diffraction intensity was measured by in-planerotating (β-rotation) the sample stage form 0 to 360°; (4) the portionformed by removing the surrounding of ±60° of the peak top from theobtained x-ray diffraction intensity plot (FIG. 1) was collinearlyapproximated by a least-square method to obtain a base line; and (5) thepeak width at the half height from the base line measured in (4) to thepeak top was defined as the half width.

(13) Observation of the Orientation State of Layered Compound in Film

Each sample was prepared by the following method and observed by atransmission electron microscope. At first, each sample film wasembedded in an epoxy resin. The epoxy resin employed was obtained bywell mixing Luveak 812, Luveak NMA (produced by Nacalai Tesque, Inc.),and DMP 30 (produced by TAAB Laboratories Equipment Ltd.) at a weightratio of 100:89:3. After the sample film was embedded in the epoxyresin, it was left for 16 hours in an oven controlled at a temperatureof 60° C. to harden the epoxy resin and obtain an embedded block.

The embedded block was attached to Ultra-cut N produced by Nissei SangyoCorporation and ultrathin specimens were produced. At first, eachspecimen was trimmed until the cross section of the portion of the filmto be observed was exposed to the resin surface by a glass knife. Next,each ultra-thin specimen was cut off by a diamond knife (Sumi KnifeSK2045, produced by Sumitomo Electric Industries Ltd.). After the cutoff ultra-tin specimen was recovered on a mesh, thin carbon vapordeposition was carried out. An electron microscope observation wascarried out using JEM-2010 produced by JEOL Ltd. under condition ofaccelerating voltage of 200 kV. The image of the cross section of thefilm obtained by the electron microscopy was recorded on an imagingplate (FDLUR-V, produced by Fujifilm Corporation). From the image, 50layered compounds were extracted at random and the inclination of therespective compounds was evaluated.

In the case the inclination dispersion of the layered compound waswithin an angle of 20° or less, it was defined the layered compound wasin-plane orientated. Those in-plane orientated were marked with ◯ andthose which were not in-plane orientated were marked with x.

(14) Thickness and Number of Total Layers in Film

Each film was cooled by liquefied nitrogen and cut off in the widthdirection of the cast film or stretched film by a Feather blade toobtain a cross section immediately after taken out. The cross sectionwas observed by an optical microscope (BX 60, produced by OlympusCorporation) and the thickness of a layer was calculated by dividing thethickness of 5 to 20 layers by the number of the layers. The number ofthe total layers was measured by the same method.

In the case the interface of layers was difficult to distinguish in theabove-mentioned method, each sample was produced by the following methodand observed by a transmission electron microscope. At first, eachsample film was embedded in an epoxy resin. The epoxy resin employed wasobtained by well mixing Luveak 812, Luveak NMA (produced by NacalaiTesque, Inc.), and DMP 30 (produced by TAAB Laboratories Equipment Ltd)at a weight ratio of 100:89:3. After the sample film was embedded in theepoxy resin, it was left for 16 hours in an oven controlled at atemperature of 60° C. to harden the epoxy resin and obtain an embeddedblock. The embedded block was attached to Ultra-cut N produced by NisseiSangyo Corporation and ultrathin specimens were produced. At first, eachspecimen was trimmed until the cross section of the portion of the filmto be observed was exposed to the resin surface by a glass knife. Next,each ultra-thin specimen was cut off by a diamond knife (Sumi KnifeSK2045, produced by Sumitomo Electric Industries Ltd.). After the cutoff ultra-tin specimen was recovered on a mesh, thin carbon vapordeposition was carried out.

An electron microscope observation was carried out using JEM-2010produced by JEOL Ltd. under condition of accelerating voltage of 200 kV.The image of the cross section of the film obtained by the electronmicroscopy was recorded on an imaging plate (FDLUR-V, produced byFujifilm Corporation). From the image, the thickness of the layer havingthe maximum thickness thicker than the interval between interfaces ofthe respective layers was measured.

(15) Oxygen Permeability (OTR)

Oxygen permeability was measured at a humidity of 65% and a temperatureof 23° C. using an oxygen permeability measurement apparatus (OX-TRAN10/50A, produced by Modern Controls, Inc.). The obtained result wasconverted into a value with a thickness of 15 μm and the value wasdefined as the oxygen permeability (OTR, cc/m²/day/atm). The conversioninto the value with a thickness of 15 μm was done according to thefollowing:

(OTR converted into value with a thickness of 15 μm)=(measuredOTR)×(film thickness, μm)/15 (μm).

(16) Piercing Strength

According to regulation of Food Sanitation Law, each sample was fixed ina cylindrical tool and a needle with a diameter of 1.0 mm and asemicircular tip end shape with a radius of 0.5 mm was thrust into thesample at a speed of 50 mm/min and the maximum load (N) until the needlepenetrated the sample was measured.

(17) Equilibrium Moisture Content

Each sample with a size of 10 cm square was dried at 60° C. for 24 hoursin vacuum and the weight (a) was measured. Thereafter, the sample wasleft in environments of 40° C. and 90% RH for 12 hours and the weight(b) was measured. The equilibrium moisture content was calculatedaccording the following expression.

Equilibrium moisture content (%)=(b−a)/a×100.

(18) Cleavage Resistance

Each film after biaxial stretching was cut out by a cutter, andSellotape (registered trademark) was stuck to the end face and left atroom temperature for 24 hours. Thereafter, the tape was peeled at anangle of 90° and existence of cleavage was confirmed.

(19) Boiling Strain

Each sample was cut in a square shape with each side of 21 cm and eachsample was left in environments of 23° C. and 65% RH for 2 hours orlonger. The length of two diagonal lines of each sample was measured anddefined as the length before treatment. Next, the sample was heated inboiling water for 30 minutes and taken out and thereafter wiped forremoving the water adhering to the surface, dried by air blow, and leftin environments of 23° C. and 65% RH for 2 hours or longer. Then, thelength of two diagonal lines of the sample was measured again anddefined as the length after treatment. The shrinkage ratio in boilingwater in 45° direction and in 135° direction was calculated from themeasured values according to the following expression and the absolutevalue (%) of the difference was defined as the boiling strain. Theaverage value of hygroscopic difference of each sample was calculated.

Shrinkage ratio in boiling water=[(length before treatment−length aftertreatment)/length before treatment]×100(%)

(20) Heat Shrinkage Ratio

The measurement was carried out according to a dimensional change testmethod described in JIS C2318, except that the test temperature wasadjusted at 160° C. and the heating time was adjusted to 10 minutes.

At first, the first invention will be described with reference toExamples and Comparative Examples.

Example 1

After pellets of a nylon 6 resin (T-800, produced by Toyobo Co., Ltd.:relative viscosity RV=2.5, containing no lubricant) and pellets of anylon 6 resin containing montmorillonite as a layered compound dispersedevenly therein (NF 3040, produced by Nanopolymer Composite Corp.;addition amount of the layered compound: 4% (inorganic material 2.6%))were respectively vacuum-dried overnight at 100° C., they were blendedat a weight ratio of 1/1. Next, the blended pellets were supplied to twoextruders. After the pellets melted at 270° C. and the same kind resinwas laminated by a static mixer having 16 elements at 275° C. and thelaminate was extruded in a sheet-like form out of a T die heated at 270°C. to cooling rolls adjusted at 20° C. and then cooled and hardened toobtain an un-stretched multilayer sheet. The ratio of the dischargeamounts of the two extruders was controlled to be 1:1. The thickness ofthe un-stretched sheet was 180 μm and the thickness of each layer in thecenter part in the width direction was about 1 μm. Tg of the sheet was35° C. and the melting point was 225° C. The sheet was at firstpreheated at 65° C., stretched 2.5 times by MD stretching at astretching temperature of 65° C. and a deformation speed of 16000%/min,and successively the sheet was continuously led to a tenter andstretched 3.8 times by TD stretching in a preheat zone at 65° C. and astretching zone at 135° C., subjected to thermal fixation at 210 and 5%transverse relaxation treatment, and thereafter, cooled, and both rimparts were cut and removed to obtain a biaxially stretched polyamideresin film with a thickness of 12 μm. The film had a width of 40 cm anda length of 1000 m and was rolled around a paper tube. The physicalproperties of the film are shown in Table 1.

Examples 2 to 5, Example 7, Comparative Examples 1, 2, and ComparativeExamples 4 to 6

The samples were produced under the conditions described in Table 1. Thefilm properties of Examples are shown in Table 1, and the filmproperties of Comparative Examples are shown in Table 2.

Example 3 and Comparative Example 1 were made to be monolayer withoutusing a static mixer. In Examples 4 and 5, TD stretching was carried outafter two-step MD stretching.

Example 6

After pellets of nylon 6 resin containing montmorillonite as a layeredcompound dispersed evenly therein (NF 3040, produced by NanopolymerComposite Corp.; addition amount of the layered compound: 4% (inorganicmaterial 2.6%)) and organically treated montmorillonite powder (Cloisite30B, produced by Southern Clay Products Inc.) were respectivelyvacuum-dried overnight at 100° C., they were blended at a weight ratioto give the addition amount of the inorganic layered compound of 8%.Thereafter, the blended pellets were supplied to two extruders andmelted and mixed at 275° C. The obtained resin pellets were again driedin a vacuum drier at 100° C. for 24 hours. The resin was supplied to anextruder and melted at 275° C. and the same kind resin was laminated bya static mixer having 16 elements at 275° C. and the laminate wasextruded in a sheet-like form out of a T die heated at 270° C. tocooling rolls adjusted at 20° C. and then cooled and hardened to obtainan un-stretched multilayer sheet. The thickness of the un-stretchedsheet was 180 μm and the thickness of each layer in the center part inthe width direction was about 1 μm. Tg of the sheet was 35° C. and themelting point was 225° C. The sheet was at first preheated at 45° C.,stretched 3.2 times by MD stretching by rolls with a surface temperatureof 85° C. and a deformation speed of 4500%/min, and successively thesheet was continuously led to a tenter and stretched 3.8 times by TDstretching in a preheat zone at 110° C. and a stretching zone at 130°C., subjected to thermal fixation at 210° C. and 5% transverserelaxation treatment, and thereafter, cooled, and both rim parts werecut and removed to obtain a biaxially stretched polyamide resin filmwith a thickness of 15 μm. The physical properties of the film are shownin Table 1.

Comparative Example 3

After pellets of a nylon 6 resin (T-800, produced by Toyobo Co., Ltd.:relative viscosity RV=2.5, containing no lubricant) and silica particlesas a lubricant (Silysia 310, produced by Fuji Silysia Chemical Ltd.)were respectively vacuum-dried overnight at 100° C., they were mixed byan extruder at 270° C. and melted and mixed at 275 to give the lubricantconcentration of 1000 ppm. The obtained resin pellets were again driedin a vacuum drier at 100° C. for 24 hours. The resin was supplied to anextruder and melted at 275° C. and the same kind resin was laminated bya static mixer having 16 elements at 275° C. and the laminate wasextruded in a sheet-like form out of a T die heated at 270° C. tocooling rolls adjusted at 20° C. and then cooled and hardened to obtainan un-stretched multilayer sheet. The thickness of the un-stretchedsheet was 180 μm and the thickness of each layer in the center part inthe width direction was about 1 μm. Tg of the sheet was 35° C. and themelting point was 225° C. The sheet was at first preheated at 45° C.,stretched 3.2 times by MD stretching by rolls with a surface temperatureof 60° C. and a deformation speed of 16000%/min, and successively thesheet was continuously led to a tenter and stretched 3.8 times by TDstretching in a preheat zone at 110° C. and a stretching zone at 130°C., subjected to thermal fixation at 210° C. and 5% transverserelaxation treatment, and thereafter, cooled, and both rim parts werecut and removed to obtain a biaxially stretched polyamide resin filmwith a thickness of 15 μm. The physical properties of the film are shownin Table 2.

TABLE 1 Examples 1 2 3 4 5 6 7 Cast Resin 1 NF3040/ NF3040 NF3040 NF3040NF3040 NF3040 + NF3040 + T800 Cloisite T800 Melting temperature 270 270275 285 290 275 270 (° C.) Resin 2 NF3040/ NF3040 — NF3040 NF3040NF3040 + NF3040 + T800 Cloisite T800 Melting temperature 270 270 — 285290 275 270 (° C.) Layer ratio 50/50 50/50 — 50/50 45/55 50/50 50/50Laminate portion 270 275 275 275 280 275 270 temperature (° C.) Addingamount of 2 4 4 4 4 8 1.5 layerd compound (%) Content of inorganic 1.32.6 2.6 2.6 2.6 5.2 1.0 material (%) Number of layers 100 or more 100 ormore 1 100 or more 100 or more 100 or more 100 or more MD Preheating 6545 40 45 45 45 45 streching temperature (° C.) Streching 65 85 70 80 8085 75 temperature (° C.) Ratio (times) 2.5 3.2 3.2 2.0, 2.0 1.5, 2.3 3.23.2 Deformation speed 16000 4500 900 1950, 1950 1200, 2700 4500 4500(%/min) Ny(A)-Ny(B) 0.006 0.003 0.002 0.004 0.002 0.003 0.003 TDPreheating temperature (° C.) 65 110 110 110 110 110 110 strechingStreching temperature (° C.) 135 130 130 135 135 130 100 Ratio (times)3.8 3.8 3.8 3 4 3.8 3.8 Thermal Temperature (° C.) 210 210 210 210 210210 210 fixation Relaxation Temperature (° C.) 210 210 210 210 210 210210 Relaxation ratio (%) 3 5 5 5 5 5 5 Properties Thickness (μm) 12 2020 15 13 15 15 The in-plane orientation ◯ ◯ ◯ ◯ ◯ ◯ ◯ state of layeredcompound Haze (%) 5 8 13 9 8 17 1.5 MD elastic modulus (GPa) 2.9 2.5 1.92.1 1.9 3.4 1.8 Surface roughness (Sa) 0.0154 0.0128 0.03 0.025 0.0240.097 0.032 Static friction coefficient μs 0.93 0.79 0.78 0.82 0.80 0.400.95 The number of pinholes 9 2 12 1 1 16 20 85-degree gloss 82 78 80 6569 64 74 In-plane orientation of 0.73 0.82 0.8 0.79 0.84 0.75 0.71layered compound Two numerical values described in one cell indicate thedata on the first and second steps of the two-steps lengthwisestrecthing in this order

TABLE 2 Comparative Examples 1 2 3 4 5 6 Cast Resin 1 NF3040 NF3040 +T800 T800 NF3040 + NF3040 T800 T800 Melting temperature (° C.) 275 270270 270 275 280 Resin 2 — NF3040 + T800 T800 NF3040 + NF3040 T800 T800Melting temperature (° C.) — 270 270 270 275 280 Layer ratio — 50/5050/50 50/50 50/50 50/50 Laminate portion 270 270 270 270 270 285temperature (° C.) Adding amount of layerd 4 0.5 0 0 2 4 compound (%)Content of inorganic 2.6 0.8 0.1 0 1.3 2.6 material (%) Number of layers1 100 or more 100 or more 100 or more 100 or more 100 or more MDPreheating temperature (° C.) 45 60 60 60 40 60 streching Strechingtemperature (° C.) 80 60 60 60 70 80 Ratio (times) 3.2 3.2 3.2 2 2.5 3.2Deformation speed (%/min) 4500 16000 16000 4500 4500 4500 Ny(A)-Ny(B)0.0008 0.008 0.008 0.008 0.0057 0.008 TD Preheating temperature (° C.)110 60 60 60 65 60 streching Streching temperature 130 135 135 135 135175 (° C.) Ratio (times) 3.8 3.8 3.8 4 2 3.8 Thermal Temperature (° C.)210 210 210 210 210 210 fixation Relaxation Temperature (° C.) 210 210210 210 210 210 Relaxation ratio (%) 5 3 3 3 3 3 Properties Thickness(μm) 20 15 15 13 15 14 The in-plane orientation ◯ ◯ — — X ◯ state oflayered compound Haze (%) 25 5 12 9 6 39 MD elastic modulus (GPa) 2.61.6 1.5 1.9 1.2 2.2 Surface roughness (Sa) 0.06 0.02 0.12 0.05 0.03 0.05Static friction coefficient μs 0.9 1.5 0.8 1.9 1.1 1.3 The number ofpinholes 18 5 2 12 17 35 85-degree gloss 51 70 49 44 54 45 In-planeorientation of 0.55 0.4 — — 0.2 0.52 layered compound

Comparative Example 7

After pellets of nylon 6 resin containing montmorillonite as a layeredcompound dispersed evenly therein (NF 3040, produced by NanopolymerComposite Corp.; addition amount of the layered compound: 4% (inorganicmaterial 2.6%)) were vacuum-dried overnight at 100° C., the same resinwas supplied to two extruders and melted at 280° C. and laminated by astatic mixer having 16 elements heated at 280° C. The laminate wasextruded in a sheet-like form out of a T die heated at 275° C. tocooling rolls adjusted at 20° C. and then cooled and hardened to obtainan un-stretched multilayer sheet. The ratio of the discharge amounts ofthe two extruders was controlled to be 1:1. The thickness of theun-stretched sheet was 150 μm, the thickness of each layer measured in across section was about 1, μm and the number of the layers was 100 orhigher. Tg of the sheet was 35° C. and the melting point was 225° C. Thesheet was at first preheated at 40° C., stretched 2 times by verticalstretching at a stretching temperature of 60° C. and a deformation speedof 2300%/min, and successively the sheet was continuously led to atenter and stretched 2 times by transverse stretching at a preheatingtemperature of 60° C. and stretching temperature of 70° C. and subjectedto thermal fixation at 210° C. and 5% transverse relaxation treatment,and thereafter, cooled, and the un-stretched part in the width directionwas cut and removed to obtain a biaxially stretched polyamide resin filmwith a thickness of 30 μm. The film had a width of 40 cm and a length of1000 m and was rolled around a paper tube. The physical properties atthat time are shown in Table 4.

Example 8

An un-stretched sheet was obtained in the same manner as ComparativeExample 7. Next, the sheet was preheated by rolls with a surfacetemperature of 45° C. and stretched 3.2 times by lengthwise stretchingusing rolls with a surface temperature of 80° C. and a deformation speedof 4500%/min, and successively the sheet was continuously led to atenter and stretched 3.8 times by transverse stretching at a preheatingtemperature of 110° C. and a stretching temperature of 135° C. andsubjected to thermal fixation at 210° C. and 5% transverse relaxationtreatment, and thereafter, cooled, and both rim parts were cut andremoved to obtain a biaxially stretched polyamide resin film with athickness of 12 μm. The film had a width of 40 cm and a length of 1000 mand was rolled around a paper tube. The physical properties at that timeare shown in Table 3. The in-plane orientation of the layered compoundwas improved from 0.2, which was of Comparative Example 7, to 0.82 andthe OTR value in conversion into 15 μm was remarkably lowered from 17 ccto 12 cc.

Example 9

After pellets of nylon 6 resin containing montmorillonite as a layeredcompound dispersed evenly therein (NF 3040, produced by NanopolymerComposite Corp.; addition amount of the layered compound: 4% (inorganicmaterial 2.6%)) were vacuum-dried overnight at 100° C., the pellets weresupplied to an extruder and melted at 290° C. After the resintemperature was adjusted at 270° in a melt-line, the melted resin wasintroduced into a static mixer with 16 elements heated at inlet part of270° C. and at center to outlet part of 285° C. and the same kind resinwas laminated. The laminate was extruded in a sheet-like form out of a Tdie heated at 280° C. to cooling rolls adjusted at 20° C. and thencooled and hardened to produce an un-stretched multilayer sheet. Thethickness of the un-stretched sheet was 200 μm and the thickness of eachlayer in the center part in the width direction was about 1 μm. Tg ofthe sheet was 40° C. The sheet was at first preheated at 45° C. andstretched by two-step stretching at a stretching temperature of 80° C.The first MD stretching was carried out at 1950%/min 2 times and thesecond MD stretching was carried out also at 1950%/min 2 times andsuccessively the sheet was continuously led to a tenter and stretched 4times by TD stretching in a preheat zone at 110° C. and a stretchingzone at 130° C., subjected to thermal fixation at 210 to 215° C. and 5%transverse relaxation treatment, and thereafter, cooled, and both rimparts were cut and removed to obtain a biaxially stretched polyamideresin film with a thickness of 15 μm. The film had a width of 40 cm anda length of 1000 m and was rolled around a paper tube. The obtained filmwas excellent in the cleavage resistance. The physical properties of thefilm are shown in Table 3. The in-plane orientation of the layeredcompound was improved from 0.2, which was of Comparative Example 7, to0.89 and the OTR value in conversion into 15 μm was remarkably loweredfrom 17 cc to 10 cc.

Examples 10 to 12

The samples were produced under the conditions described in Table 3. Thefilm properties are shown in Table 3. Along with improvement of thein-plane orientation of the layered compound, the OTR value inconversion into 15 μm was improved to be around 12 cc.

Comparative Example 8

After pellets of nylon 6 resin containing montmorillonite as a layeredcompound dispersed evenly therein (NF 3040, produced by NanopolymerComposite Corp.; addition amount of the layered compound: 4% (inorganicmaterial 2.6%)) were vacuum-dried overnight at 100° C. Film formationwas carried out using a monolayer inflation film formation apparatus.The pellets were supplied to an extruder and melted at 290° C. Next, thefilm was extruded out of a circular die heated at 280° C. and cooledwith air and simultaneously, the discharge amount, rolling speed, andtube diameter were so adjusted as to control the stretching ratio of 4times on the basis of the area. The center part of the tube was cut toobtain a biaxially stretched polyamide resin film with a thickness of 20μm. The physical properties at that time are shown in Table 4.

Comparative Example 9

After pellets of poly(ethylene terephthalate) resin (RE 553, produced byToyobo Co., Ltd.) and a powder of montmorillonite (Cloisite 10A,produced by Southern Clay Products Inc.) as a layered compound wererespectively vacuum-dried overnight at 100° C., they were dry-blended ata weight ratio of 85/15 and supplied to two extruders and melted andmixed at 295° C. The obtained resin pellets were again dried in a vacuumdrier at 100° C. for 24 hours. The resin was supplied to an extruder andmelted at 295° C. and the same kind resin was laminated by a staticmixer having 16 elements at 285° C. The laminate was extruded in asheet-like form out of a T die heated at 285° C. to cooling rollsadjusted at 20° C. and then cooled and hardened to obtain anun-stretched multilayer sheet. The thickness of the un-stretched sheetwas 100 μm and the thickness of each layer in the center part in thewidth direction was about 1 μm. Tg of the sheet was 65° C. The sheet wasat first preheated at 90° C., stretched 2 times by MD stretching byrolls with a surface temperature of 110° C. and a deformation speed of2500%/min, and successively the sheet was continuously led to a tenterand stretched 2 times by TD stretching in a preheat zone at 90° C. and astretching zone at 100° C., subjected to thermal fixation at 230° C. and5% transverse relaxation treatment, and thereafter, cooled, and both rimparts were cut and removed to obtain a biaxially stretched poly(ethyleneterephthalate) resin film with a thickness of 25 μm. The film had awidth of 40 cm and a length of 1000 m and was rolled around a papertube. The physical properties of the film are shown in Table 4.

Reference Example 1

A biaxially stretched poly(ethylene terephthalate) resin film wasobtained in the same manner as Comparative Example 9, except that thethickness of the sheet before stretching was 400 μm, the MD stretchingratio was 4 times, and the TD stretching ratio was 4 times. The film hada width of 40 cm and a length of 1000 m and was rolled around a papertube. The physical properties of the film are shown in Table 3. Ascompared with Comparative Example 9, along with improvement of thein-plane orientation, the storage elastic modulus at 100° C. in thedynamic viscoelasticity of the obtained film was increased about doublefrom 20 MPa to 50 MPa and the heat resistance was improved.

Comparative Example 10

After pellets of polypropylene resin (Noblen FS2011, produced bySumitomo Chemical Co., Ltd.) and a powder of organically treatedmontmorillonite (Cloisite 30B, produced by Southern Clay Products Inc.)as a layered compound were dry-blended at a weight ratio of 80/20 andsupplied to two extruders and melted and mixed at 270° C. The obtainedresin pellets were dried in a vacuum drier at 100° C. for 24 hours. Theresin was supplied to an extruder and melted at 275° C. and the samekind resin was laminated by a static mixer having 16 elements at 275° C.The laminate was extruded in a sheet-like form out of a T die heated at275° C. to cooling rolls adjusted at 20° C. and then cooled and hardenedto obtain an un-stretched multilayer sheet. The thickness of theun-stretched sheet was 150 μm and the thickness of each layer in thecenter part in the width direction was about 1 μm. The sheet was atfirst preheated at 50° C., stretched 2 times by MD stretching by rollswith a surface temperature of 130° and a deformation speed of 3000%/min,and successively the sheet was continuously led to a tenter andstretched 2 times by TD stretching in a preheat zone at 160° C. and astretching zone at 165° C., subjected to thermal fixation at 155° C. and5% transverse relaxation treatment, and thereafter, cooled, and both rimparts were cut and removed to obtain a biaxially stretched polypropyleneresin film with a thickness of 25 μm. The film had a width of 40 cm anda length of 1000 m and was rolled around a paper tube. The physicalproperties of the film are shown in Table 4.

Reference Example 2

A biaxially stretched polypropylene resin film was obtained in the samemanner as Comparative Example 10, except that the thickness of the sheetbefore stretching was made to be 1000 μm, the MD stretching ratio was 6times, and the TD stretching ratio was 8 times. The film had a width of40 cm and a length of 1000 m and was rolled around a paper tube. Thephysical properties of the film are shown in Table 3. The in-planeorientation was sufficiently high and, for example, it was expected thatthe gas barrier property and heat resistance were improved.

Reference Example 3

After pellets of a MXD6 type polyamide resin containing montmorilloniteas a layered compound evenly dispersed therein (Imperm 105, produced byNanocor, Inc., layered compound addition amount: 7%) were vacuum-driedovernight at 100° C., the pellets were supplied to an extruder andmelted at 280° C., a static mixer with 16 elements heated at 280° C. wasintroduced in a melt-line, and the same kind resin was laminated. Thelaminate was extruded in a sheet-like form out of a T die heated at 270°C. to cooling rolls adjusted at 20° C. and then cooled and hardened toproduce an un-stretched multilayer sheet. The thickness of theun-stretched sheet was 200 μm and the thickness of each layer in thecenter part in the width direction was about 1 μm. The sheet was atfirst preheated at 80° C. and stretched at a stretching temperature of100° C. and a deformation speed of 5000%/min and ratio of 3.5 times andsuccessively the sheet was continuously led to a tenter and stretched3.5 times by TD stretching in a preheat zone at 80° C. and a stretchingzone at 95° C., subjected to thermal fixation at 180° C. and 3%transverse relaxation treatment, and thereafter, cooled, and both rimparts were cut and removed to obtain a biaxially stretched polyamideresin film with a thickness of 15 μm. The film had a width of 40 cm anda length of 1000 m and was rolled around a paper tube. The physicalproperties of the film are shown in Table 3.

TABLE 3 Examples Reference Examples 8 9 10 11 12 1 2 3 Cast Resin 1NF3040 NF3040 NF3040 NF3040 NF3040 + RE553 + FS2011 + Imperm 105Cloisite Cloisite 10A Cliisite Melting temperature 280 290 275 275 275295 275 280 (° C.) Resin 2 NF3040 NF3040 NF3040 NF3040 + NF3040 +RE553 + FS2011 + Imperm 105 T800 (50/50) Cloisite Cloisite 10A CliisiteMelting temperature (° C.) 280 290 275 285 275 295 275 280 Layer ratio50/50 50/50 50/50 70/30 50/50 50/50 50/50 50/50 Laminate portiontemperature 280 270/285 275 275 275 285 275 280 (° C.) Adding amount oflayerd 4 4 4 3.4 8 15 5 7 compound (%) Content of inorganic material 2.62.6 2.6 2.2 5.2 15 3.2 5 (%) Number of layers 100 or 100 or more 100 ormore 8 100 or 100 or more 100 or 100 or more more more more MDPreheating temperature 45 45 45 45 45 90 50 80 streching (° C.)Streching temperature 80 80 80 80 85 110 135 100 (° C.) Ratio (times)3.2 2.0, 2.0 3.2 3.2 3.2 4.0 6.0 3.5 Deformation speed (%/min) 45001950, 1950 16000 4500 4500 5000 9000 5000 TD Preheating temperature (°C.) 110 110 110 110 110 90 160 80 streching Streching temperature (° C.)135 130 130 135 130 100 165 95 Ratio (times) 3.8 4.0 3.8 3.0 3.8 4.0 8.03.5 Thermal Temperature (° C.) 210 210 210 210 210 230 155 180 fixationRelaxation Temperature (° C.) 210 210 210 210 210 230 155 180 Relaxationratio (%) 5 5 5 5 5 5 5 3 Properties Thickness (μm) 12 15 18 18 15 25 2515 The in-plane orientation ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ state of layered compoundHaze (%) 11 10 11 11 15 20 10 19 MD elastic modulus (GPa) 2.7 2.7 2.92.5 2.8 3.8 Surface roughness (Sa) 0.0124 0.0118 0.0140 0.0100 0.08000.062 Static friction coefficient μs 0.78 0.78 0.81 0.77 0.83 0.54 Thenumber of pinholes 2 1 2 1 14 18 In-plane orientation of 0.82 0.89 0.760.81 0.52 0.72 0.88 0.62 layered compound OTR (cc/m2/day/atm) 12 10 1212 7 25 — 1 High temperature MD 1.3 1.2 1.3 1.0 1.5 1.3 — 1.8 elasticmodulus (MPa) Measurement temperature 80 80 80 80 80 100 — 80 (° C.)

TABLE 4 Comparative Examples 7 8 9 10 Cast Resin 1 NF3040 NF3040 RE553 +FS2011 + Cloisite 10A Cloisite 30B Melting temperature (° C.) 280 275295 275 Resin 2 NF3040 — RE553 + NF3040 + Cloisite 10A Cloisite 30BMelting temperature (° C.) 280 — 295 275 Layer ratio 50/50 — 50/50 50/50Laminate portion temperature (° C.) 280 275 285 275 Adding amount oflayerd compound (%) 4 4 15 5 Content of inorganic material (%) 2.6 2.615 3.3 Number of layers 100 or more 1 100 or more 100 or more MDPreheating temperature (° C.) 40 — 90 50 streching Streching temperature(° C.) 60 — 110 130 Ratio (times) 2.0 2 2.0 2.0 Deformation speed(%/min) 4500 — 2500 3000 TD Preheating temperature (° C.) 60 — 90 160streching Streching temperature (° C.) 70 — 100 165 Ratio (times) 2.0 22.0 2.0 Thermal Temperature (° C.) 210 — 230 155 fixation RelaxationTemperature (° C.) 210 — 230 155 Relaxation ratio (%) 5 — 5 5 PropertiesThickness (μm) 30 20 25 25 The in-plane orientation state of x x x xlayered compound Haze (%) 13 8 30 17 MD elastic modulus (GPa) 1.2 0.8Surface roughness (Sa) 0.03 0.005 Static friction coefficient μs 1.1 1.8The number of pinholes 17 5 In-plane orientation of layered 0.2 0.1 orless 0.2 0.2 compound OTR (cc/m2/day/atm) 17 20 44 — High temperature MDelastic 0.7 0.6 0.8 — modulus (M Pa) Measurement temperature (° C.) 8080 100 — (Attention) Since Cloisite 10A does not containe organictreatment agent, adding amount of layerd compound is equal to content ofinorganic material

Example 13

After pellets of nylon 6 resin containing montmorillonite as a layeredcompound dispersed evenly therein (NF 3040, produced by NanopolymerComposite Corp.; addition amount of the layered compound: 4% (inorganicmaterial 2.6%)) were vacuum-dried overnight at 100° C., the pellets weresupplied to two extruders and melted at 285° C. and the same resin waslaminated by a static mixer having 10 elements heated at 285° C. Thelaminate was extruded in a sheet-like form out of a T die heated at 280°C. to cooling rolls adjusted at 20° C. and then cooled and hardened toobtain an un-stretched multilayer sheet. The ratio of the dischargeamounts of the two extruders was controlled to be 1:1. The thickness ofthe un-stretched sheet was 240 μm and the thickness of each layer in thecenter part in the width direction was about 1 μm. Tg of the sheet was35° C. and the melting point was 225° C. The sheet was at firstpreheated at 45° C., stretched 3.5 times by MD stretching at stretchingtemperature of 85° C. and a deformation speed of 4500%/min, andsuccessively the sheet was continuously led to a tenter and stretched3.8 times by TD stretching in a preheat zone at 65° C. and a stretchingzone at 135° C., subjected to thermal fixation at 210° C. and 5%transverse relaxation treatment, and thereafter, cooled, and both rimparts were cut and removed to obtain a biaxially stretched polyamideresin film with a thickness of 18 μm. The film had a width of 40 cm anda length of 1000 m and was rolled around a paper tube. The physicalproperties of the film are shown in Table 5.

Examples 14 to 18

The samples were produced under the conditions described in Table 5. InExamples 15, 17, and 18, TD stretching was carried out after two-step MDstretching. The each film had a width of 40 cm and a length of 1000 mand was rolled around a paper tube. The physical properties of the filmsare shown in Table 5.

Reference Example 4

After pellets of nylon 6 resin containing montmorillonite as a layeredcompound dispersed evenly therein (NF 3040, produced by NanopolymerComposite Corp.; addition amount of the layered compound: 4% (inorganicmaterial 2.6%)) and organically treated montmorillonite powder (Cloisite30B, produced by Southern Clay Products Inc.) were respectivelyvacuum-dried overnight at 100° C., they were dry-blended at a weightratio of 92/8. Thereafter, the blended pellets were supplied to twoextruders and melted and mixed at 285° C. The obtained resin pelletswere again dried in a vacuum drier at 100° C. for 24 hours. The resinwas supplied to an extruder and melted at 285° C. and the same kindresin was laminated by a static mixer with 16 elements at 280° C. Thelaminate was extruded in a sheet-like form out of a T die heated at 270°C. to cooling rolls adjusted at 20° C. and then cooled and hardened toobtain an un-stretched multilayer sheet. The thickness of theun-stretched sheet was 180 μm and the thickness of each layer in thecenter part in the width direction was about 1 μm. Tg of the sheet was35° C. and the melting point was 225° C. The sheet was at firstpreheated at 45° C., stretched 3.0 times by MD stretching by rolls witha surface temperature of 85° C. and a deformation speed of 2000%/min,and successively the sheet was continuously led to a tenter andstretched 3.8 times by TD stretching in a preheat zone at 110° C. and astretching zone at 135° C., subjected to thermal fixation at 210° C. and5% transverse relaxation treatment, and thereafter, cooled, and both rimparts were cut and removed to obtain a biaxially stretched polyamideresin film with a thickness of 15 μm. The film had a width of 40 cm anda length of 1000 m and was rolled around a paper tube. The physicalproperties of the film are shown in Table 5.

Comparative Example 11

After pellets of nylon 6 resin containing montmorillonite as a layeredcompound dispersed evenly therein (NF 3040, produced by NanopolymerComposite Corp.; addition amount of the layered compound: 4%) werevacuum-dried overnight at 100° C. Film formation was carried out using amonolayer inflation film formation apparatus. The pellets were suppliedto an extruder and melted at 275° C. Next, the film was extruded out ofa circular die heated at 275° C. and cooled with air and simultaneously,the discharge amount, rolling speed, and tube diameter were so adjustedas to control the stretching ratio of 2 times on the basis of the area.The center part of the tube was cut to obtain a biaxially stretchedpolyamide resin film with a thickness of 15 μm. The physical propertiesat that time are shown in Table 6.

Comparative Examples 12 to 14

The samples were produced under the conditions described in Table 6. InExamples 12 and 14, no static mixer was used and the films were made tobe monolayer. The each film had a width of 40 cm and a length of 1000 mand was rolled around a paper tube. The physical properties of the filmsare shown in Table 6.

TABLE 5 Reference Examples Example 13 14 15 16 17 18 4 Cast Resin 1NF3040 NF3040 + NF3040 NF3040 NF3040 NF3040 NF3040 + T800 (50/50)Cloisite 30B Melting temperature (° C.) 285 285 285 285 290 290 285Resin 2 NF3040 NF3040 + NF3040 T814 NF3040 NF3040 NF3040 + T800 (50/50)Cloisite 30B Melting temperature (° C.) 285 285 285 270 290 290 285Layer ratio 50/50 50/50 50/50 25/75 45/55 50/50 50/50 Laminate portion285 285 275 270 275 280 280 temperature (° C.) Adding amount of layerd 42 4 1 4 4 12 compound (%) Content of inorganic material 2.6 1.3 2.6 0.92.6 2.6 8 (%) Number of layers 100 or more 100 or more 100 or more 100or more 100 or more 100 or more 100 or more MD Preheating temperature (°C.) 45 65 45 60 45 45 45 streching Streching temperature (° C.) 85 85 7080 80 85 85 Ratio (times) 3.5 2.5 2.0 × 2.0 3.5 1.5 × 1.8 2.0 × 2.2 3.0Deformation speed (%/min) 4500 16000 1950 + 1950 4500 1200 + 2700 1950 +1950 2000 Ny(A)-Ny(B) 0.003 0.006 0.003 0.006 0.003 0.003 0.003 TDPreheating temperature (° C.) 65 110 110 70 110 110 110 strechingStreching temperature (° C.) 135 135 140 70 140 140 135 Ratio (times)3.8 3.8 4.0 3.8 4.0 4.0 3.8 Thermal Temperature (° C.) 210 210 210 210210 210 210 fixation Relaxation Temperature (° C.) 210 210 210 210 210210 210 Relaxation ratio (%) 5 3 5 5 5 5 5 Properties Thickness (μm) 1813 12 15 12 8 15 The in-plane orientation state ◯ ◯ ◯ ◯ ◯ ◯ ◯ of layeredcompound Haze (%) 11 5 13 3 10 16 17 MD elastic modulus (GPa) 2.5 2.42.9 2.5 2.5 2.9 2.8 Surface roughness (Sa) 0.0125 0.015 0.021 0.03000.018 0.0125 0.0800 Static friction coefficient μs 0.73 0.93 0.65 0.440.72 0.74 0.75 The number of pinholes 1 6 2 2 1 1 15 In-planeorientation of 0.81 0.70 0.86 0.64 0.59 0.85 0.52 layered compoundIn-plane orientation (ΔP) 0.060 0.059 0.065 0.065 0.057 0.063 0.057Piercing strength/thickness 1.1 0.9 1.3 0.9 1.3 1.8 0.9 (N/um) T800:Polyamide resin produced by Toyobo Co., Ltd.: RV = 2.5, containing nolubricant T814: Polyamide resin produced by Toyobo Co., Ltd.: RV = 2.5,silica content 3500 ppm

TABLE 6 Comparative Examples 11 12 13 14 Cast Resin 1 NF3040 T814 NF3040NF3040 Melting temperature (° C.) 275 270 275 275 Resin 2 — — NF3040 —Melting temperature (° C.) — — 275 — Layer ratio — — 50/50 — Laminateportion temperature (° C.) 275 270 270 270 Adding amount of layerdcompound (%) 4 0 4 4 Content of inorganic material (%) 2.6 0.35 2.6 2.6Number of layers 1 1 100 or more 1 MD Preheating temperature (° C.) — 6045 40 streching Streching temperature (° C.) — 60 80 70 Ratio (times)1.4 3.2 1.5 3 Deformation speed (%/min) — 4500 1500 4500 Ny(A) · Ny(B) —0.007 0.001 0.000 TD Preheating temperature (° C.) — 60 110 55 strechingStreching temperature (° C.) — 70 130 70 Ratio (times) 1.4 3.8 2.0 2.5Thermal Temperature (° C.) — 210 210 210 fixation Relaxation Temperature(° C.) — 210 210 210 Relaxation ratio (%) — 5 5 3 Properties Thickness(μm) 15 15 18 18 The in-plane orientation state of x — x x layeredcompound Haze (%) 9 3 10 11 MD elastic modulus (GPa) 0.8 1.5 0.9 0.8Surface roughness (Sa) 0.0050 0.1200 0.1500 0.0300 Static frictioncoefficient μs 1.8 0.8 1.1 1.2 The number of pinholes 5 2 25 14 In-planeorientation of layered 0.1 or less — 0.1 or less 0.33 compound In-planeorientation (ΔP) 0.003 0.06 0.055 0.056 Piercing strength/thickness(N/μm) 0.5 0.7 0.6 0.65

Example 19

After pellets of nylon 6 resin containing montmorillonite as a layeredcompound dispersed evenly therein (NF 3040, produced by NanopolymerComposite Corp.; addition amount of the layered compound: 4%) werevacuum-dried overnight at 100° C., the same resin was supplied to twoextruders and melted at 280° C. and laminated by a static mixer with 16elements at 280° C. The laminate was extruded in a sheet-like form outof a T die heated at 275° C. to cooling rolls adjusted at 20° C. andthen cooled and hardened to obtain an un-stretched multilayer sheet. Theratio of the discharge amounts of the two extruders was controlled to be1:1. The thickness of the un-stretched sheet was 180 μm and thethickness of each layer was found about 1 μm in the cross section andthe number of the layers was 100 or more. Tg of the sheet was 35° C. andthe melting point was 225° C. The sheet was at first preheated at 45°C., stretched 3.2 times by lengthwise stretching at a stretchingtemperature of 85° C. and a deformation speed of 4500%/min, andsuccessively the sheet was continuously led to a tenter and stretched3.8 times by transverse stretching in a preheat zone at 110° C. and astretching zone at 130° C., subjected to thermal fixation at 210° C. and5% transverse relaxation treatment, and thereafter, cooled, and theun-stretched part in the width direction was cut and removed to obtain abiaxially stretched polyamide resin film with a thickness of 18 μM. Thefilm had a width of 40 cm and a length of 1000 m and was rolled around apaper tube. The physical properties of the film are shown in Table 7.

Examples 20 and 21 and Comparative Examples 16 to 18

The samples were produced in the same manner as Example 19 under theconditions described in Table 7. The film properties are shown in Table7. In Example 21, a multilayer sheet was produced by using a staticmixer with 6 elements and in Comparative Example 18, a sample wasproduced from a monolayer sheet by using a feed block with a monolayerstructure.

Comparative Example 15

After pellets of nylon 6 resin containing montmorillonite as a layeredcompound dispersed evenly therein (NF 3040, produced by NanopolymerComposite Corp.; addition amount of the layered compound: 4%) werevacuum-dried overnight at 100° C. Film formation was carried out using amonolayer inflation film formation apparatus. The pellets were suppliedto an extruder and melted at 290° C. Next, the film was extruded out ofa circular die heated at 280° C. and cooled with air and simultaneously,the discharge amount, rolling speed, and tube diameter were so adjustedas to control the stretching ratio of 4 times on the basis of the area.The center part of the tube was cut to obtain a biaxially stretchedpolyamide resin film with a thickness of 15 μm. The film had a width of40 cm and a length of 1000 m and was rolled around a paper tube. Thephysical properties at that time are shown in Table 7.

TABLE 7 Examples Comparative Examples 19 20 21 15 16 17 18 Cast Resin 1NF3040 NF3040 NF3040 NF3040 T814 NF3040 + NF3040 + T814 T814 (50/50)(12.5/87.5) Melting temperature (° C.) 280 285 285 290 270 280 280 Resin2 NF3040 NF3040 NF3040 — T814 NF3040 + NF3040 + T814 T814 (50/50)(12.5/87.5) Melting temperature 280 285 285 — 270 280 280 (° C.) Layerratio 50/50 50/50 50/50 — 50/50 50/50 50/50 Laminate portion 280 280 280280 270 270 270 temperature (° C.) Adding amount of layerd 4 4 4 4 0 20.5 compound (%) Content of inorganic material 2.6 2.6 2.6 2.6 0.35 1.50.6 (%) Number of layers 100 or more 100 or more 60 1 100 or more 100 ormore 1 MD Preheating temperature (° C.) 45 45 40 — 60 60 45 strechingStreching temperature (° C.) 85 80 80 — 60 60 60 Ratio (times) 3.2 3.23.2 2 3.0 2.0 3.0 Deformation speed (%/min) 4500 4500 4500 — 4300 43004500 Ny(A)-Ny(B) 0.003 0.003 0.003 — 0.008 0.003 0.003 TD Preheatingtemperature (° C.) 110 110 80 — 110 110 60 streching Strechingtemperature (° C.) 130 135 100 — 130 130 110 Ratio (times) 3.8 3.8 3.5 24.0 2.5 4.0 Thermal Temperature (° C.) 210 210 210 — 210 210 210fixation Relaxation Temperature (° C.) 210 210 210 — 210 210 210Relaxation ratio (%) 5 5 5 — 3 3 5 Properties Thickness (μm) 18 20 15 1515 18 19 The in-plane orientation state of ◯ ◯ ◯ X — X ◯ layeredcompound Haze (%) 12.1 12.0 8.2 5.2 1.8 8 23 MD elastic modulus (GPa)2.5 2.5 2.5 0.8 1.5 2.4 1.5 Surface roughness (Sa) 0.0140 0.0130 0.01300.0050 0.1200 0.0210 0.1300 Static friction coefficient μs 0.68 0.650.66 1.8 0.8 0.93 0.79 The number of pinholes 2 2 4 5 2 6 1 In-planeorientation of layered 0.81 0.82 0.49 0.1 or less — 0.7 0.64 compoundEquilibrium moisture content (%) 3.3 3.5 4.5 5.0 2.6 3.8 2.9 Maximumpoint stress × Elongation 18595 20765 27294 13724 13546 13565 15543 at40% RH (X1, MPa* %) Maximum point stress × Elongation 19686 23601 3520922233 32230 26451 35594 at 80% RH (X2, MPa* %) X2/X1 1.06 1.14 1.29 1.622.38 1.95 2.29 In-plane orientation (ΔP) 0.0060 0.0061 0.0062 0.0030.0061 0.0055 0.0059 T814: Polyamide resin produced by Toyobo Co., Ltd.:RV = 2.5, silica content 3500 ppm

Next, the second invention will be described with reference to Examplesand Comparative Examples.

Example 22

After pellets of nylon 6 resin (T-814, produced by Toyobo Co., Ltd.:relative viscosity RV=2.8, containing a lubricant) were vacuum-driedovernight at 100° C., the same resin pellets were supplied to twoextruders and melted at 270° C. and the same kind resin was laminated bya static mixer having 10 elements. The laminate was extruded in asheet-like form out of a T die to cooling rolls adjusted at 20° C. andthen cooled and hardened to obtain an un-stretched multilayer sheet. Theratio of the discharge amounts of the two extruders was controlled to be1:1. The thickness of the un-stretched sheet was 250 μm and thethickness of each layer measured in a cross section was about 1 μm. Tgof the sheet was 35° C. and the melting point was 225° C. The sheet wasat first preheated at 40° C., stretched 3.2 times by lengthwisestretching at a stretching temperature of 60° C., and successively thesheet was continuously led to a tenter and stretched 3.8 times bytransverse stretching at a preheating temperature of 60° C. and astretching temperature of 130° C. and subjected to thermal fixation at210° C. and 5% transverse relaxation treatment, and thereafter, cooled,and both rim parts were cut and removed to obtain a biaxially stretchedpolyamide resin film with a thickness of 14 μm. The film had a width of40 cm and a length of 1000 m and was rolled around a paper tube. Thephysical properties at that time are shown in Table 8.

Examples 23 to 31 and Comparative Examples 19 to 26

In Examples 24 and 25, un-stretched sheets with a 8-layer structure wereproduced by using a feed block with a 8-layer structure: in ComparativeExamples 19 to 20, 23, and 25 to 26, un-stretched sheets with amonolayer structure were produced by using a feed block with a monolayerstructure: in Comparative Example 21, an un-stretched sheet with a16-layer structure was produced: in Examples 23, 24, 25, 26, and 27 andComparative Example 23, samples were produced under the conditionsdescribed in Table 8 and in the same manner as Example 22, except TDstretching was carried out after two-step MD stretching. The filmproperties are shown in Table 8 for Examples 23 and 24, in Table 9 forExamples 25 to 31, in Table 8 for Comparative Examples 19 to 23, and inTable 10 for Comparative Examples 24 to 26, respectively.

Comparative Example 27

After pellets of nylon 6 resin containing montmorillonite as a layeredcompound dispersed evenly therein (NF 3040, produced by NanopolymerComposite Corp.; addition amount of the layered compound; 4%) werevacuum-dried overnight at 100° C. Film formation was carried out using amonolayer inflation film formation apparatus. The pellets were suppliedto an extruder and melted at 280° C. Next, the film was extruded out ofa circular die heated at 280° C. and cooled with air and simultaneously,the discharge amount, rolling speed, and tube diameter were so adjustedas to control the stretching ratio of 4 times on the basis of the area.The center part of the tube was cut to obtain a biaxially stretchedpolyamide resin film with a thickness of 25 μM. The physical propertiesat that time are shown in Table 10.

Example 32

Pellets of nylon 6 resin (T-814, produced by Toyobo Co., Ltd.; relativeviscosity RV=28, containing a lubricant), pellets of nylon 6 resincontaining montmorillonite as a layered compound dispersed evenlytherein (NF 3040, produced by Nanopolymer Composite Corp.; additionamount of the layered compound; 4%), and pellet of MXD6 type nylon resincopolymerized with m-xylylenediamine and excellent in the barrierproperty were vacuum-dried overnight at 100° C. In a configuration thata static mixer with 16 elements heated at 275° C. was introduced into amelt line between an extruder at the skin layer side and a feed block ofa film formation apparatus capable of laminating of two-kindthree-layers, the pellets of T814 and NF3040 blended by dry blend at aratio of 50/50 were supplied to two extruders at the skin layer side andS6001 was supplied to an extruder at the core layer side. The resins atthe skin layer side were melted at 270° C. and the resin at the corelayer side was melted at 280° C. and a structure (multilayer structure)in which a monolayer sheet was sandwiched by two sheets with multilayerstructure was formed by a feed block heated at 275° C. The resultinglaminate was extruded in a sheet-like form out of a T die to coolingrolls adjusted at 20° C. and then cooled and hardened to obtain anun-stretched multilayer sheet. The ratio of the discharge amounts of thethree extruders was controlled to be 45:10:45. The thickness of theun-stretched sheet was 250 μm and the thickness of each layer at theskin layer side measured in a cross section was about 1 μm. The sheetwas at first preheated at 70° C., stretched 3.2 times by lengthwisestretching at a stretching temperature of 80° C. and a deformation speedof 4500%/min, and successively the sheet was continuously led to atenter and stretched 3.8 times by transverse stretching at a preheating110° C. and thereafter at 135° C. and subjected to thermal fixation at210° C. and 5% transverse relaxation treatment, and thereafter, cooled,and both rim parts were cut and removed to obtain a biaxially stretchedpolyamide resin film with a thickness of 15 μm. The film had a width of40 cm and a length of 1000 m and was rolled around a paper tube. Thephysical properties at that time are shown in Table 10.

TABLE 8 Examples Comparative Examples 22 23 24 19 20 21 22 23 Cast Resin1 T814 T814 T814 T814 T814 T814 T814 T814 Melting temperature (° C.) 270270 270 270 270 270 270 270 Resin 2 T814 T814 S6001 — — — NF3040 —Melting temperature (° C.) 270 270 285 — — — 275 — Layer ratio 50/5050/50 90/10 — — — 75/25 — Laminate portion temperature 270 270 270 270270 270 270 270 (° C.) Adding amount of layerd 0 0 0 0 0 0 1 0 compound(%) Content of inorganic material 0.35 0.35 0.32 0.35 0.35 0.35 1.350.35 (%) Number of layers 100 or more 100 or more 8 1 1 16 100 or more 1MD Preheating temperature (° C.) 40 45 45 40 40 40 40 45 strechingStreching temperature (° C.) 60 60 60 60 60 80 70 60 Ratio (times) 3.22.0, 2.0 2.0, 2.0 2 5.5 2 3 1.75, 1.75 Deformation speed (%/min) 90004500, 4500 4500, 4500 4500 4500 4500 4500 1900, 1900 Ny(A)-Ny(B) 0.00650.0062 0.0062 0.006 0.008 0.004 0.006 0.004 TD Preheating temperature (°C.) 60 60 60 60 60 60 60 60 streching Streching temperature (° C.) 130130 130 130 130 130 130 130 Ratio (times) 8.8 4 4 2 2.5 5 3.5 4 ThermalTemperature (° C.) 210 210 210 210 210 210 210 210 fixation RelaxationTemperature (° C.) 210 210 210 210 210 210 210 210 Relaxation ratio (%)5 3 5 5 5 5 5 5 Properties Thickness (μm) 14 15 15 18 16 15 15 14 Thein-plane orientation state — — — — — — ◯ — of layered compound Haze (%)3 3 3.1 3 3 4 5 2 MD elastic modulus (GPa) 1.5 1.6 1.8 1.2 1.3 1.5 1.91.4 Surface roughness (Sa) 0.12 0.10 0.10 0.11 0.12 0.12 0.09 0.12Static friction coefficient μs 0.8 0.9 1.1 0.8 0.7 0.8 0.75 0.8 Thenumber of pinholes 2 1 4 1 2 2 2 2 In-plane orientation of layered — — —— — — 0.52 — compound In-plane orientation (ΔP) 0.063 0.064 0.062 0.040.06 0.051 0.062 0.063 Boiling strain (%) 0.7 0.4 0.9 0.4 2.8 2.5 2.92.2 Heat shrinkage ratio (%) 1.2 1.3 1.2 1.5 1.6 1.9 1.0 2OTR(cc/m²/day/atm) 22 22 12 22 22 22 18 22 T800: Polyamide resinproduced by Toyobo Co., Ltd.: RV = 2.5, containing no lubricant T814:Polyamide resin produced by Toyobo Co., Ltd.: RV = 2.5, silica content3500 ppm

TABLE 9 Examples 25 26 27 28 29 30 31 Cast Resin 1 NF3040 NF3040 NF3040NF3040 NF3040 NF3040 + NF3040 T814 (50/50) Melting temperature (° C.)280 280 280 280 280 280 280 Resin 2 NF3040 NF3040 NF3040 NF3040 NF3040NF3040 + NF3040 T814 (50/50) Melting temperature (° C.) 280 280 280 280280 280 280 Layer ratio 50/50 55/45 50/50 50/50 50/50 50/50 50/50Laminate portion temperature 285 280 285 300 310 290 310 (° C.) Addingamount of layerd 4 4 4 4 4 2 4 compound (%) Content of inorganicmaterial (%) 2.6 2.6 2.6 2.6 2.6 1.5 2.6 Number of layers 8 100 or more100 or more 100 or more 100 or more 100 or more 100 or more MDPreheating temperature (° C.) 45 45 45 45 45 45 45 streching Strechingtemperature (° C.) 80 80 80 85 85 80 80 Ratio (times) 2.0 × 2.0 1.5 ×2.3 2.3 × 1.5 3.2 3.2 3.2 2.0 × 2.0 Deformation speed (%/min) 1950 +1950 1200 + 2700 2700 + 1200 4500 4500 4500 1950 + 1950 Ny(A)-Ny(B)0.004 0.002 0.004 0.003 0.003 0.003 0.003 TD Preheating temperature (°C.) 110 110 110 110 110 100 110 streching Streching temperature (° C.)135 135 135 130 130 125 130 Ratio (times) 3 4 4 3.8 3.8 3.8 4.5 ThermalTemperature (° C.) 210 210 210 215 210 210 210 fixation RelaxationTemperature (° C.) 210 210 210 210 210 210 210 Relaxation ratio (%) 5 55 5 5 5 3 Properties Thickness (μm) 15 13 14 18 18 15 14 The in-planeorientation state of ◯ ◯ ◯ ◯ ◯ ◯ ◯ layered compound Haze (%) 10 10 11 1414 8 6.5 In-plane orientation (ΔP) 0.059 0.061 0.064 0.061 0.06 0.0650.064 MD elastic modulus (GPa) 2.4 1.9 1.9 2.5 2.5 2 2.7 Surfaceroughness (Sa) 0.025 0.024 0.024 0.0128 0.0128 0.015 0.015 Staticfriction coefficient μs 0.82 0.8 0.8 0.79 0.79 0.94 0.8 The number ofpinholes 2 1 1 3 3 6 1 In-plane orientation of layered 0.55 0.81 0.840.8 0.82 0.74 0.88 compound Boiling strain (%) 0.9 0.7 1.3 1.7 1.4 0.90.6 Heat shrinkage ratio (%) 1.3 1.2 0.9 0.1 0.2 0.8 0.3OTR(cc/m²/day/atm) 11 12 10 11 10.5 14.5 14

TABLE 10 Comparative Examples Example 24 25 26 27 32 Cast Resin 1 (skinlayer side) NF3040 NF3040 NF3040 + NF3040 NF3040 + T814 (50/50) T814(50/50) Melting temperature (° C.) 280 280 280 280 270 Resin 2 (skinlayer side) NF3040 — — — NF3040 + T814 (50/50) Melting temperature (°C.) 260 — — — 270 Resin 3(core layer side) — — — — S6001 Meltingtemperature (° C.) — — — — 280 Layer ratio 50/0/50 — — — 45/10/45Laminate portion temperature of resin 285 280 285 280 275 1 and resin 2(° C.) Laminate portion temperature of — — — — 275 resins 1-3 (° C.)Adding amount of layerd compound 4 4 2 4 1.8 (%) Content of inorganicmaterial (%) 2.6 2.6 1.5 2.6 1.3 Number of layers 100 or more 1 1 1 100or more MD Preheating temperature (° C.) 45 45 45 — 70 strechingStreching temperature (° C.) 85 85 80 — 80 Ratio (times) 4 3 3 2 3.2Deformation speed (%/min) 4800 4500 500 — 4500 Ny(A)-Ny(B) 0.001 0.0000.000 — 0.003 TD Preheating temperature (° C.) 110 110 110 — 110streching Streching temperature (° C.) 135 135 135 — 135 Ratio (times) 22 3.5 2 3.8 Thermal Temperature (° C.) 210 210 210 — 210 fixationRelaxation Temperature (° C.) 210 210 210 — 210 Relaxation ratio (%) 5 55 — 5 Properties Thickness (μm) 18 20 18 25 15 The in-plane orientationstate X X ◯ X of layered compound Haze (%) 10 25 40 3 7 MD elasticmodulus (GPa) 0.9 0.9 2.2 0.7 2.6 Surface roughness (Sa) 0.15 0.14 0.0140.005 0.18 Static friction coefficient μs 1.1 1.12 0.78 1.8 0.45 Thenumber of pinholes 25 35 14 5 2 In-plane orientation of layered 0.2 0.10.45 0.1 or less 0.66 compound In-plane orientation (ΔP) 0.0062 0.0550.056 0.056 0.006 Boiling strain (%) 3.4 2.2 3.4 2 1.6 Heat shrinkageratio (%) 2.1 2.5 3.3 1.0 1.0 OTR(cc/m²/day/atm) 30 15 25 2.0 10

INDUSTRIAL APPLICABILITY

A conventional nylon film is made easy to slip by roughing the surfacein the case the slipping property under high humidity is requiredbecause the slipping property fluctuates in accordance with thehumidity; however according to the first invention, since a filmcontaining an inorganic layered compound has little alteration of theslipping property in accordance with humidity and also exhibitssufficient slipping property even if the surface roughness is small,contradictory characteristics such as gloss can be simultaneouslysatisfied together. The layered compound is in-plane orientated to ahigh level, so that the effect of improving various characteristics canbe extracted to the ultimate extent and the film is excellent inappearance, has high productivity and industrially highly valuable.Further, the obtained film is excellent in the barrier property,dimensional stability, mechanical characteristics, and piercing strengthand it is made possible to produce a film having improved mechanicalcharacteristics in low humidity and lowered humidity dependence of theimpact strength at a low speed with a high productivity, so that thefilm can be used for use for which a conventional film has beendifficult to be employed and thus preferably usable as industrialmaterials other than wrapping materials for food, drug, and generalgoods.

Further, a conventional biaxially stretched polyamide resin film showssignificant boiling strain due to bowing if the in-plane orientation isincreased for improving the mechanical characteristics. In the case ofthe biaxially stretched multilayer polyamide resin film of the secondinvention, the boiling strain in the end parts in the film widthdirection is diminished by lowering the stretching stress andproductivity of films with low boiling strain can be improved.Furthermore, addition of the layered compound to each layer makes itpossible to produce a film excellent in not only the boiling strain butalso mechanical characteristics and barrier property.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 X-ray diffraction chart of Example 8.

1. A biaxially stretched polyamide resin film containing 0.3 to 10 wt. %of an inorganic material including an layered compound, wherein thelayered compound is in-plane oriented and the film has a haze of 1.0 to20%, an elastic modulus in the longitudinal direction of 1.7 to 3.5 GPaat a relative humidity of 35% RH, a surface roughness (Sa) of 0.01 to0.1 and a static friction coefficient (F/B) of 0.3 to 1.0 at a normalstress of 0.5 N/cm².
 2. The biaxially stretched polyamide resin film asdescribed in claim 1, wherein the number of pinholes after 1000 timesGelbo Flex test at 23° C. is 0 to
 30. 3. The biaxially stretchedpolyamide resin film as described in claim 1, wherein the film istransversely stretched at a transverse stretching temperature of 50 to155° C.
 4. The biaxially stretched polyamide resin film as described inclaim 1, wherein the thermoplastic resin stretched film contains 0.3 to10 wt. % of the inorganic material including the layered compound andhas a laminate structure of 8 or more layers in total and a thickness of3 to 200 μm, and the in-plane orientation degree of the inorganiclayered compound measured by x-ray diffractometry is in a range of 0.4to 1.0.
 5. The biaxially stretched polyamide multilayer resin film asdescribed in claim 4, wherein a static mixer method is employed at thetime of melt extrusion of a thermoplastic resin and the resintemperature immediately before introduction into the static mixer is ina range from the melting point to melting point +70° C. and the heatertemperature in the latter half of the static mixer is set to be higherby 5° C. or more and by 40° C. or less than the resin temperatureimmediately before introduction into the static mixer.
 6. The biaxiallystretched polyamide resin film containing 0.3 to 10 wt. % of theinorganic material including the layered compound as described in claim1, wherein the layered compound is in-plane oriented and the in-planeorientation (ΔP) of the film is 0.057 to 0.075, and the value ofpiercing strength/thickness of the film is 0.88 to 2.50 (N/μm).
 7. Thebiaxially stretched polyamide resin film as described in claim 6,wherein the stretching ratio on the basis of an area by biaxialstretching measured as the product of the stretching ratio in thelengthwise direction and the stretching ratio in the transversedirection is 8.5 times or more.
 8. The biaxially stretched polyamideresin film as described in claim 6, wherein biaxial stretching issuccessive biaxial stretching in lengthwise stretching-transversestretching order and when Ny is defined as a refractive index in thecenter part in the width direction of the film, the differenceNy(A)−Ny(B) between Ny(A) which is Ny of the sheet before lengthwisestretching and Ny(B) which is Ny of the sheet after uniaxial stretchingis 0.003 or higher.
 9. The biaxially stretched polyamide resin film asdescribed in claim 1, wherein the film contains 0.3 to 10 wt. % of theinorganic material including the layered compound and has a laminatestructure of 8 or more layers, the film is obtained by stretching asmuch as 2.5 to 5.0 times in the longitudinal direction and 3.0 to 5.0times in the width direction, and the film has a ratio of the product(X1) of the maximum point stress (MPa) and a breaking elongation (%) ofa sample stored at a humidity of 40% for 12 hours and the product (X2)of the maximum point stress (MPa) and a breaking elongation (%) of asample stored at a relative humidity of 80% for 12 hours is in a rangeof 1.0 to 1.5 when the maximum point stress and breaking elongation ismeasured by a method as described in JIS K 7113 under conditions of astarting length of 40 mm, a width of 10 mm, and a deformation rate of200 mm/min after storage at an equilibrium water absorption ratio of 3.0to 7.0% and a relative humidity of 40%.
 10. A biaxially stretchedmultilayer polyamide resin film having 8 or more layers in total andusing a same resin composition for 80% based on the ratio of the numberof the layers, wherein the film is stretched 2.5 to 5.0 times in thelongitudinal direction of the film and has an in-plane orientationcoefficient (ΔP) of 0.057 to 0.07 and a strain of 0.1 to 2.0% afterboiling treatment.
 11. The biaxially stretched multilayer polyamideresin film as described in claim 10, wherein the film contains 0.3 to 10wt. % of an inorganic material containing a layered compound, thelayered compound is in-plane oriented, and the oxygen permeation amountin conversion into 15 μm is 0.05 to 18 cc.
 12. The biaxially stretchedmultilayer polyamide resin film as described in claim 10, wherein atleast one layer or more of resin layers containing a polyamide resinhaving a meta-xylylene skeleton as a main component are laminated. 13.The biaxially stretched polyamide resin film as described in claim 2,wherein the film is transversely stretched at a transverse stretchingtemperature of 50 to 155° C.
 14. The biaxially stretched polyamide resinfilm as described in claim 7, wherein biaxial stretching is successivebiaxial stretching in lengthwise stretching-transverse stretching orderand when Ny is defined as a refractive index in the center part in thewidth direction of the film, the difference Ny(A)−Ny(B) between Ny(A)which is Ny of the sheet before lengthwise stretching and Ny(B) which isNy of the sheet after uniaxial stretching is 0.003 or higher.
 15. Thebiaxially stretched multilayer polyamide resin film as described inclaim 11, wherein at least one layer or more of resin layers containinga polyamide resin having a meta-xylylene skeleton as a main componentare laminated.